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 $163.79   7.201%   $175.5845   $175.58   $175.60   $175.60  
  Purchase #2 $203.77   6.567%   $217.1516   $217.15   $217.15   $217.20  
  Purchase #3 $120.98   13.128%   $136.8623   $136.86   $136.85   $136.90  
  Purchase #4 $172.91   10.344%   $190.7958   $190.80   $190.80   $190.80  
  Purchase #5 $6.45   4.822%   $6.761   $6.76   $6.75   $6.80  
  Purchase #6 $111.48   6.603%   $118.841   $118.84   $118.85   $118.80  
  Purchase #7 $167.77   5.593%   $177.1534   $177.15   $177.15   $177.20  
  7 purchase totals = $947.15       $1,023.1496   $1,023.14   $1,023.15   $1,023.30