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 $32.85   5.763%   $34.7431   $34.74   $34.75   $34.70  
  Purchase #2 $162.76   7.588%   $175.1102   $175.11   $175.10   $175.10  
  Purchase #3 $202.26   10.340%   $223.1737   $223.17   $223.15   $223.20  
  Purchase #4 $111.45   9.214%   $121.719   $121.72   $121.70   $121.70  
  Purchase #5 $151.78   12.197%   $170.2926   $170.29   $170.30   $170.30  
  Purchase #6 $119.66   12.173%   $134.2262   $134.23   $134.25   $134.20  
  Purchase #7 $35.29   7.679%   $37.9999   $38.00   $38.00   $38.00  
  7 purchase totals = $816.05       $897.2647   $897.26   $897.25   $897.20