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 $240.34   5.571%   $253.7293   $253.73   $253.75   $253.70  
  Purchase #2 $240.94   11.428%   $268.4746   $268.47   $268.45   $268.50  
  Purchase #3 $49.80   8.498%   $54.032   $54.03   $54.05   $54.00  
  Purchase #4 $75.52   7.208%   $80.9635   $80.96   $80.95   $81.00  
  Purchase #5 $206.71   8.822%   $224.946   $224.95   $224.95   $224.90  
  Purchase #6 $205.82   12.647%   $231.8501   $231.85   $231.85   $231.90  
  Purchase #7 $24.47   6.211%   $25.9898   $25.99   $26.00   $26.00  
  7 purchase totals = $1,043.60       $1,139.9853   $1,139.98   $1,140.00   $1,140.00