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 $89.55   5.359%   $94.349   $94.35   $94.35   $94.30  
  Purchase #2 $84.96   8.223%   $91.9463   $91.95   $91.95   $91.90  
  Purchase #3 $19.40   4.847%   $20.3403   $20.34   $20.35   $20.30  
  Purchase #4 $245.89   8.156%   $265.9448   $265.94   $265.95   $265.90  
  Purchase #5 $98.34   12.367%   $110.5017   $110.50   $110.50   $110.50  
  Purchase #6 $69.37   6.835%   $74.1114   $74.11   $74.10   $74.10  
  Purchase #7 $157.25   11.310%   $175.035   $175.04   $175.05   $175.00  
  7 purchase totals = $764.76       $832.2285   $832.23   $832.25   $832.00