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 $239.72   13.863%   $272.9524   $272.95   $272.95   $273.00  
  Purchase #2 $7.42   4.444%   $7.7497   $7.75   $7.75   $7.70  
  Purchase #3 $214.94   9.390%   $235.1229   $235.12   $235.10   $235.10  
  Purchase #4 $35.49   4.816%   $37.1992   $37.20   $37.20   $37.20  
  Purchase #5 $239.91   11.407%   $267.2765   $267.28   $267.30   $267.30  
  Purchase #6 $120.75   13.644%   $137.2251   $137.23   $137.25   $137.20  
  Purchase #7 $102.36   3.760%   $106.2087   $106.21   $106.20   $106.20  
  7 purchase totals = $960.59       $1,063.7345   $1,063.74   $1,063.75   $1,063.70