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 $203.98   10.667%   $225.7385   $225.74   $225.75   $225.70  
  Purchase #2 $55.95   11.624%   $62.4536   $62.45   $62.45   $62.50  
  Purchase #3 $86.66   9.435%   $94.8364   $94.84   $94.85   $94.80  
  Purchase #4 $181.26   13.755%   $206.1923   $206.19   $206.20   $206.20  
  Purchase #5 $196.32   5.847%   $207.7988   $207.80   $207.80   $207.80  
  Purchase #6 $16.50   9.331%   $18.0396   $18.04   $18.05   $18.00  
  Purchase #7 $162.38   11.628%   $181.2615   $181.26   $181.25   $181.30  
  7 purchase totals = $903.05       $996.3207   $996.32   $996.35   $996.30