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 $236.89   13.533%   $268.9483   $268.95   $268.95   $268.90  
  Purchase #2 $195.97   3.205%   $202.2508   $202.25   $202.25   $202.30  
  Purchase #3 $202.52   13.550%   $229.9615   $229.96   $229.95   $230.00  
  Purchase #4 $71.74   11.402%   $79.9198   $79.92   $79.90   $79.90  
  Purchase #5 $231.31   5.447%   $243.9095   $243.91   $243.90   $243.90  
  Purchase #6 $43.57   12.278%   $48.9195   $48.92   $48.90   $48.90  
  Purchase #7 $195.37   13.490%   $221.7254   $221.73   $221.75   $221.70  
  7 purchase totals = $1,177.37       $1,295.6348   $1,295.64   $1,295.60   $1,295.60