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 $92.81   8.553%   $100.748   $100.75   $100.75   $100.70  
  Purchase #2 $9.59   7.302%   $10.2903   $10.29   $10.30   $10.30  
  Purchase #3 $53.60   9.650%   $58.7724   $58.77   $58.75   $58.80  
  Purchase #4 $88.87   8.680%   $96.5839   $96.58   $96.60   $96.60  
  Purchase #5 $194.36   5.203%   $204.4726   $204.47   $204.45   $204.50  
  Purchase #6 $65.75   11.212%   $73.1219   $73.12   $73.10   $73.10  
  Purchase #7 $153.42   3.668%   $159.0474   $159.05   $159.05   $159.00  
  7 purchase totals = $658.40       $703.0365   $703.03   $703.00   $703.00