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 $116.93   12.389%   $131.4165   $131.42   $131.40   $131.40  
  Purchase #2 $62.45   3.506%   $64.6395   $64.64   $64.65   $64.60  
  Purchase #3 $108.77   9.139%   $118.7105   $118.71   $118.70   $118.70  
  Purchase #4 $151.31   12.238%   $169.8273   $169.83   $169.85   $169.80  
  Purchase #5 $143.28   5.628%   $151.3438   $151.34   $151.35   $151.30  
  Purchase #6 $169.40   3.616%   $175.5255   $175.53   $175.55   $175.50  
  Purchase #7 $236.26   4.659%   $247.2674   $247.27   $247.25   $247.30  
  7 purchase totals = $988.40       $1,058.7305   $1,058.74   $1,058.75   $1,058.60