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 $49.87   4.232%   $51.9805   $51.98   $52.00   $52.00  
  Purchase #2 $175.77   5.560%   $185.5428   $185.54   $185.55   $185.50  
  Purchase #3 $97.38   11.343%   $108.4258   $108.43   $108.45   $108.40  
  Purchase #4 $64.75   5.789%   $68.4984   $68.50   $68.50   $68.50  
  Purchase #5 $236.97   4.662%   $248.0175   $248.02   $248.00   $248.00  
  Purchase #6 $149.66   3.545%   $154.9654   $154.97   $154.95   $155.00  
  Purchase #7 $231.97   6.510%   $247.0712   $247.07   $247.05   $247.10  
  7 purchase totals = $1,006.37       $1,064.5016   $1,064.51   $1,064.50   $1,064.50