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 $168.43   8.835%   $183.3108   $183.31   $183.30   $183.30  
  Purchase #2 $174.79   10.719%   $193.5257   $193.53   $193.55   $193.50  
  Purchase #3 $113.55   10.310%   $125.257   $125.26   $125.25   $125.30  
  Purchase #4 $109.78   10.535%   $121.3453   $121.35   $121.35   $121.30  
  Purchase #5 $88.83   4.137%   $92.5049   $92.50   $92.50   $92.50  
  Purchase #6 $74.44   12.659%   $83.8634   $83.86   $83.85   $83.90  
  Purchase #7 $196.64   8.399%   $213.1558   $213.16   $213.15   $213.20  
  7 purchase totals = $926.46       $1,012.9629   $1,012.97   $1,012.95   $1,013.00