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 $26.31   3.793%   $27.3079   $27.31   $27.30   $27.30  
  Purchase #2 $151.38   4.775%   $158.6084   $158.61   $158.60   $158.60  
  Purchase #3 $119.71   13.511%   $135.884   $135.88   $135.90   $135.90  
  Purchase #4 $212.78   6.106%   $225.7723   $225.77   $225.75   $225.80  
  Purchase #5 $191.50   11.679%   $213.8653   $213.87   $213.85   $213.90  
  Purchase #6 $138.64   8.561%   $150.509   $150.51   $150.50   $150.50  
  Purchase #7 $228.63   13.119%   $258.624   $258.62   $258.60   $258.60  
  7 purchase totals = $1,068.95       $1,170.5709   $1,170.57   $1,170.50   $1,170.60