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 $91.83   6.774%   $98.0506   $98.05   $98.05   $98.10  
  Purchase #2 $209.40   5.348%   $220.5987   $220.60   $220.60   $220.60  
  Purchase #3 $221.84   6.534%   $236.335   $236.34   $236.35   $236.30  
  Purchase #4 $204.53   5.350%   $215.4724   $215.47   $215.45   $215.50  
  Purchase #5 $237.41   10.553%   $262.4639   $262.46   $262.45   $262.50  
  Purchase #6 $64.68   12.151%   $72.5393   $72.54   $72.55   $72.50  
  Purchase #7 $41.75   9.270%   $45.6202   $45.62   $45.60   $45.60  
  7 purchase totals = $1,071.44       $1,151.0801   $1,151.08   $1,151.05   $1,151.10