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 $68.31   11.570%   $76.2135   $76.21   $76.20   $76.20  
  Purchase #2 $100.46   12.285%   $112.8015   $112.80   $112.80   $112.80  
  Purchase #3 $233.49   3.666%   $242.0497   $242.05   $242.05   $242.00  
  Purchase #4 $124.44   7.268%   $133.4843   $133.48   $133.50   $133.50  
  Purchase #5 $134.41   11.874%   $150.3698   $150.37   $150.35   $150.40  
  Purchase #6 $186.42   4.124%   $194.108   $194.11   $194.10   $194.10  
  Purchase #7 $101.28   11.199%   $112.6223   $112.62   $112.60   $112.60  
  7 purchase totals = $948.81       $1,021.6491   $1,021.64   $1,021.60   $1,021.60