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 $128.28   10.550%   $141.8135   $141.81   $141.80   $141.80  
  Purchase #2 $160.94   3.388%   $166.3926   $166.39   $166.40   $166.40  
  Purchase #3 $168.93   10.842%   $187.2454   $187.25   $187.25   $187.20  
  Purchase #4 $108.30   11.769%   $121.0458   $121.05   $121.05   $121.00  
  Purchase #5 $102.98   13.734%   $117.1233   $117.12   $117.10   $117.10  
  Purchase #6 $142.56   9.831%   $156.5751   $156.58   $156.60   $156.60  
  Purchase #7 $18.36   7.281%   $19.6968   $19.70   $19.70   $19.70  
  7 purchase totals = $830.35       $909.8925   $909.90   $909.90   $909.80