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 $82.85   13.295%   $93.8649   $93.86   $93.85   $93.90  
  Purchase #2 $15.83   8.760%   $17.2167   $17.22   $17.20   $17.20  
  Purchase #3 $225.57   7.647%   $242.8193   $242.82   $242.80   $242.80  
  Purchase #4 $175.88   7.874%   $189.7288   $189.73   $189.75   $189.70  
  Purchase #5 $235.49   10.572%   $260.386   $260.39   $260.40   $260.40  
  Purchase #6 $226.80   9.392%   $248.1011   $248.10   $248.10   $248.10  
  Purchase #7 $9.29   5.774%   $9.8264   $9.83   $9.85   $9.80  
  7 purchase totals = $971.71       $1,061.9432   $1,061.95   $1,061.95   $1,061.90