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 $54.45   8.805%   $59.2443   $59.24   $59.25   $59.20  
  Purchase #2 $199.75   6.869%   $213.4708   $213.47   $213.45   $213.50  
  Purchase #3 $234.49   5.272%   $246.8523   $246.85   $246.85   $246.90  
  Purchase #4 $84.28   12.113%   $94.4888   $94.49   $94.50   $94.50  
  Purchase #5 $197.79   7.515%   $212.6539   $212.65   $212.65   $212.70  
  Purchase #6 $101.85   6.817%   $108.7931   $108.79   $108.80   $108.80  
  Purchase #7 $26.87   11.175%   $29.8727   $29.87   $29.85   $29.90  
  7 purchase totals = $899.48       $965.3759   $965.36   $965.35   $965.50