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 $83.84   12.144%   $94.0215   $94.02   $94.00   $94.00  
  Purchase #2 $42.83   7.714%   $46.1339   $46.13   $46.15   $46.10  
  Purchase #3 $120.67   11.106%   $134.0716   $134.07   $134.05   $134.10  
  Purchase #4 $170.39   7.801%   $183.6821   $183.68   $183.70   $183.70  
  Purchase #5 $225.75   11.211%   $251.0588   $251.06   $251.05   $251.10  
  Purchase #6 $236.75   3.619%   $245.318   $245.32   $245.30   $245.30  
  Purchase #7 $15.62   11.481%   $17.4133   $17.41   $17.40   $17.40  
  7 purchase totals = $895.85       $971.6992   $971.69   $971.65   $971.70