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 $205.88   8.614%   $223.6145   $223.61   $223.60   $223.60  
  Purchase #2 $6.94   10.484%   $7.6676   $7.67   $7.65   $7.70  
  Purchase #3 $162.89   10.403%   $179.8354   $179.84   $179.85   $179.80  
  Purchase #4 $64.83   4.772%   $67.9237   $67.92   $67.90   $67.90  
  Purchase #5 $14.62   12.145%   $16.3956   $16.40   $16.40   $16.40  
  Purchase #6 $53.32   7.439%   $57.2865   $57.29   $57.30   $57.30  
  Purchase #7 $175.78   10.434%   $194.1209   $194.12   $194.10   $194.10  
  7 purchase totals = $684.26       $746.8442   $746.85   $746.80   $746.80