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 $53.67   3.111%   $55.3397   $55.34   $55.35   $55.30  
  Purchase #2 $129.39   8.737%   $140.6948   $140.69   $140.70   $140.70  
  Purchase #3 $57.50   10.428%   $63.4961   $63.50   $63.50   $63.50  
  Purchase #4 $202.98   12.150%   $227.6421   $227.64   $227.65   $227.60  
  Purchase #5 $238.39   13.501%   $270.575   $270.58   $270.60   $270.60  
  Purchase #6 $138.98   10.408%   $153.445   $153.45   $153.45   $153.40  
  Purchase #7 $33.43   11.197%   $37.1732   $37.17   $37.15   $37.20  
  7 purchase totals = $854.34       $948.3659   $948.37   $948.40   $948.30