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 $98.52   4.668%   $103.1189   $103.12   $103.10   $103.10  
  Purchase #2 $63.91   11.376%   $71.1804   $71.18   $71.20   $71.20  
  Purchase #3 $22.26   10.389%   $24.5726   $24.57   $24.55   $24.60  
  Purchase #4 $68.73   4.331%   $71.7067   $71.71   $71.70   $71.70  
  Purchase #5 $59.47   7.539%   $63.9534   $63.95   $63.95   $64.00  
  Purchase #6 $235.84   3.195%   $243.3751   $243.38   $243.40   $243.40  
  Purchase #7 $197.53   3.292%   $204.0327   $204.03   $204.05   $204.00  
  7 purchase totals = $746.26       $781.9398   $781.94   $781.95   $782.00