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 $26.39   12.749%   $29.7545   $29.75   $29.75   $29.80  
  Purchase #2 $39.43   4.870%   $41.3502   $41.35   $41.35   $41.40  
  Purchase #3 $154.93   13.477%   $175.8099   $175.81   $175.80   $175.80  
  Purchase #4 $120.69   8.140%   $130.5142   $130.51   $130.50   $130.50  
  Purchase #5 $149.57   11.657%   $167.0054   $167.01   $167.00   $167.00  
  Purchase #6 $16.60   9.265%   $18.138   $18.14   $18.15   $18.10  
  Purchase #7 $154.82   5.266%   $162.9728   $162.97   $162.95   $163.00  
  7 purchase totals = $662.43       $725.5450   $725.54   $725.50   $725.60