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 $44.61   8.178%   $48.2582   $48.26   $48.25   $48.30  
  Purchase #2 $184.84   6.758%   $197.3315   $197.33   $197.35   $197.30  
  Purchase #3 $110.31   9.809%   $121.1303   $121.13   $121.15   $121.10  
  Purchase #4 $93.67   9.450%   $102.5218   $102.52   $102.50   $102.50  
  Purchase #5 $24.42   5.468%   $25.7553   $25.76   $25.75   $25.80  
  Purchase #6 $233.28   12.862%   $263.2845   $263.28   $263.30   $263.30  
  Purchase #7 $113.89   11.457%   $126.9384   $126.94   $126.95   $126.90  
  7 purchase totals = $805.02       $885.2200   $885.22   $885.25   $885.20