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 $88.85   3.119%   $91.6212   $91.62   $91.60   $91.60  
  Purchase #2 $27.38   7.822%   $29.5217   $29.52   $29.50   $29.50  
  Purchase #3 $231.95   4.238%   $241.78   $241.78   $241.80   $241.80  
  Purchase #4 $89.49   5.313%   $94.2446   $94.24   $94.25   $94.20  
  Purchase #5 $235.41   9.802%   $258.4849   $258.48   $258.50   $258.50  
  Purchase #6 $22.61   12.473%   $25.4301   $25.43   $25.45   $25.40  
  Purchase #7 $70.75   4.556%   $73.9734   $73.97   $73.95   $74.00  
  7 purchase totals = $766.44       $815.0559   $815.04   $815.05   $815.00