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 $64.34   8.148%   $69.5824   $69.58   $69.60   $69.60  
  Purchase #2 $151.52   10.808%   $167.8963   $167.90   $167.90   $167.90  
  Purchase #3 $7.54   5.129%   $7.9267   $7.93   $7.95   $7.90  
  Purchase #4 $11.71   4.683%   $12.2584   $12.26   $12.25   $12.30  
  Purchase #5 $108.27   13.283%   $122.6515   $122.65   $122.65   $122.70  
  Purchase #6 $247.37   8.163%   $267.5628   $267.56   $267.55   $267.60  
  Purchase #7 $149.33   6.315%   $158.7602   $158.76   $158.75   $158.80  
  7 purchase totals = $740.08       $806.6383   $806.64   $806.65   $806.80