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 $212.26   13.417%   $240.7389   $240.74   $240.75   $240.70  
  Purchase #2 $194.51   5.571%   $205.3462   $205.35   $205.35   $205.30  
  Purchase #3 $21.62   5.267%   $22.7587   $22.76   $22.75   $22.80  
  Purchase #4 $203.49   3.460%   $210.5308   $210.53   $210.55   $210.50  
  Purchase #5 $116.50   5.746%   $123.1941   $123.19   $123.20   $123.20  
  Purchase #6 $172.63   3.751%   $179.1054   $179.11   $179.10   $179.10  
  Purchase #7 $60.56   8.680%   $65.8166   $65.82   $65.80   $65.80  
  7 purchase totals = $981.57       $1,047.4907   $1,047.50   $1,047.50   $1,047.40