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 $55.92   5.316%   $58.8927   $58.89   $58.90   $58.90  
  Purchase #2 $88.86   7.521%   $95.5432   $95.54   $95.55   $95.50  
  Purchase #3 $225.80   12.536%   $254.1063   $254.11   $254.10   $254.10  
  Purchase #4 $224.25   6.746%   $239.3779   $239.38   $239.40   $239.40  
  Purchase #5 $212.93   4.754%   $223.0527   $223.05   $223.05   $223.10  
  Purchase #6 $235.38   11.385%   $262.178   $262.18   $262.20   $262.20  
  Purchase #7 $123.86   6.607%   $132.0434   $132.04   $132.05   $132.00  
  7 purchase totals = $1,167.00       $1,265.1942   $1,265.19   $1,265.25   $1,265.20