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 $48.26   7.568%   $51.9123   $51.91   $51.90   $51.90  
  Purchase #2 $200.46   13.146%   $226.8125   $226.81   $226.80   $226.80  
  Purchase #3 $141.58   3.237%   $146.1629   $146.16   $146.15   $146.20  
  Purchase #4 $164.48   8.838%   $179.0167   $179.02   $179.00   $179.00  
  Purchase #5 $153.81   6.208%   $163.3585   $163.36   $163.35   $163.40  
  Purchase #6 $244.89   4.517%   $255.9517   $255.95   $255.95   $256.00  
  Purchase #7 $120.96   5.474%   $127.5814   $127.58   $127.60   $127.60  
  7 purchase totals = $1,074.44       $1,150.7960   $1,150.79   $1,150.75   $1,150.90