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 $60.58   5.282%   $63.7798   $63.78   $63.80   $63.80  
  Purchase #2 $217.91   12.287%   $244.6846   $244.68   $244.70   $244.70  
  Purchase #3 $197.52   3.292%   $204.0224   $204.02   $204.00   $204.00  
  Purchase #4 $83.58   11.223%   $92.9602   $92.96   $92.95   $93.00  
  Purchase #5 $114.91   3.571%   $119.0134   $119.01   $119.00   $119.00  
  Purchase #6 $207.32   3.152%   $213.8547   $213.85   $213.85   $213.90  
  Purchase #7 $12.26   10.165%   $13.5062   $13.51   $13.50   $13.50  
  7 purchase totals = $894.08       $951.8213   $951.81   $951.80   $951.90