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 $47.62   10.753%   $52.7406   $52.74   $52.75   $52.70  
  Purchase #2 $28.65   3.463%   $29.6421   $29.64   $29.65   $29.60  
  Purchase #3 $188.73   8.244%   $204.2889   $204.29   $204.30   $204.30  
  Purchase #4 $239.40   13.675%   $272.138   $272.14   $272.15   $272.10  
  Purchase #5 $8.99   13.393%   $10.194   $10.19   $10.20   $10.20  
  Purchase #6 $6.25   9.501%   $6.8438   $6.84   $6.85   $6.80  
  Purchase #7 $175.36   7.475%   $188.4682   $188.47   $188.45   $188.50  
  7 purchase totals = $695.00       $764.3156   $764.31   $764.35   $764.20