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 $69.67   10.133%   $76.7297   $76.73   $76.75   $76.70  
  Purchase #2 $87.55   4.351%   $91.3593   $91.36   $91.35   $91.40  
  Purchase #3 $223.72   11.674%   $249.8371   $249.84   $249.85   $249.80  
  Purchase #4 $92.92   5.173%   $97.7268   $97.73   $97.75   $97.70  
  Purchase #5 $144.80   7.397%   $155.5109   $155.51   $155.50   $155.50  
  Purchase #6 $10.68   11.743%   $11.9342   $11.93   $11.95   $11.90  
  Purchase #7 $235.95   12.400%   $265.2078   $265.21   $265.20   $265.20  
  7 purchase totals = $865.29       $948.3058   $948.31   $948.35   $948.20