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 $48.32   13.315%   $54.7538   $54.75   $54.75   $54.80  
  Purchase #2 $214.86   6.585%   $229.0085   $229.01   $229.00   $229.00  
  Purchase #3 $31.81   12.471%   $35.777   $35.78   $35.80   $35.80  
  Purchase #4 $104.95   4.848%   $110.038   $110.04   $110.05   $110.00  
  Purchase #5 $200.28   6.306%   $212.9097   $212.91   $212.90   $212.90  
  Purchase #6 $102.86   11.398%   $114.584   $114.58   $114.60   $114.60  
  Purchase #7 $204.30   7.614%   $219.8554   $219.86   $219.85   $219.90  
  7 purchase totals = $907.38       $976.9264   $976.93   $976.95   $977.00