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 $49.93   10.529%   $55.1871   $55.19   $55.20   $55.20  
  Purchase #2 $115.53   11.545%   $128.8679   $128.87   $128.85   $128.90  
  Purchase #3 $54.75   4.742%   $57.3462   $57.35   $57.35   $57.30  
  Purchase #4 $225.91   5.158%   $237.5624   $237.56   $237.55   $237.60  
  Purchase #5 $141.92   6.263%   $150.8084   $150.81   $150.80   $150.80  
  Purchase #6 $140.62   13.843%   $160.086   $160.09   $160.10   $160.10  
  Purchase #7 $143.32   9.279%   $156.6187   $156.62   $156.60   $156.60  
  7 purchase totals = $871.98       $946.4767   $946.49   $946.45   $946.50