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 $218.72   7.783%   $235.743   $235.74   $235.75   $235.70  
  Purchase #2 $14.53   5.253%   $15.2933   $15.29   $15.30   $15.30  
  Purchase #3 $138.54   6.777%   $147.9289   $147.93   $147.95   $147.90  
  Purchase #4 $106.60   8.287%   $115.4339   $115.43   $115.45   $115.40  
  Purchase #5 $197.26   3.185%   $203.5427   $203.54   $203.55   $203.50  
  Purchase #6 $162.54   5.146%   $170.9043   $170.90   $170.90   $170.90  
  Purchase #7 $59.56   13.725%   $67.7346   $67.73   $67.75   $67.70  
  7 purchase totals = $897.75       $956.5807   $956.56   $956.65   $956.40