Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $219.29   13.424%   $248.7275   $248.73   $248.75   $248.70  
  Purchase #2 $201.84   13.689%   $229.4699   $229.47   $229.45   $229.50  
  Purchase #3 $146.81   6.191%   $155.899   $155.90   $155.90   $155.90  
  Purchase #4 $237.36   3.482%   $245.6249   $245.62   $245.60   $245.60  
  Purchase #5 $154.26   11.195%   $171.5294   $171.53   $171.55   $171.50  
  Purchase #6 $201.57   9.406%   $220.5297   $220.53   $220.55   $220.50  
  Purchase #7 $86.58   13.195%   $98.0042   $98.00   $98.00   $98.00  
  7 purchase totals = $1,247.71       $1,369.7846   $1,369.78   $1,369.80   $1,369.70