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 $62.42   11.825%   $69.8012   $69.80   $69.80   $69.80  
  Purchase #2 $245.42   7.210%   $263.1148   $263.11   $263.10   $263.10  
  Purchase #3 $211.66   5.350%   $222.9838   $222.98   $223.00   $223.00  
  Purchase #4 $112.52   8.339%   $121.903   $121.90   $121.90   $121.90  
  Purchase #5 $243.98   10.849%   $270.4494   $270.45   $270.45   $270.40  
  Purchase #6 $154.47   9.781%   $169.5787   $169.58   $169.60   $169.60  
  Purchase #7 $177.92   3.401%   $183.9711   $183.97   $183.95   $184.00  
  7 purchase totals = $1,208.39       $1,301.8020   $1,301.79   $1,301.80   $1,301.80