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 $86.59   7.763%   $93.312   $93.31   $93.30   $93.30  
  Purchase #2 $47.44   8.608%   $51.5236   $51.52   $51.50   $51.50  
  Purchase #3 $71.33   9.139%   $77.8488   $77.85   $77.85   $77.80  
  Purchase #4 $211.87   10.823%   $234.8007   $234.80   $234.80   $234.80  
  Purchase #5 $180.58   13.673%   $205.2707   $205.27   $205.25   $205.30  
  Purchase #6 $247.84   3.212%   $255.8006   $255.80   $255.80   $255.80  
  Purchase #7 $11.95   12.814%   $13.4813   $13.48   $13.50   $13.50  
  7 purchase totals = $857.60       $932.0377   $932.03   $932.00   $932.00