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 $100.73   3.867%   $104.6252   $104.63   $104.65   $104.60  
  Purchase #2 $83.94   12.235%   $94.2101   $94.21   $94.20   $94.20  
  Purchase #3 $26.90   4.517%   $28.1151   $28.12   $28.10   $28.10  
  Purchase #4 $188.35   9.266%   $205.8025   $205.80   $205.80   $205.80  
  Purchase #5 $185.74   6.757%   $198.2905   $198.29   $198.30   $198.30  
  Purchase #6 $240.88   10.499%   $266.17   $266.17   $266.15   $266.20  
  Purchase #7 $167.50   4.205%   $174.5434   $174.54   $174.55   $174.50  
  7 purchase totals = $994.04       $1,071.7568   $1,071.76   $1,071.75   $1,071.70