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 $123.92   6.797%   $132.3428   $132.34   $132.35   $132.30  
  Purchase #2 $246.77   7.722%   $265.8256   $265.83   $265.85   $265.80  
  Purchase #3 $239.45   10.592%   $264.8125   $264.81   $264.80   $264.80  
  Purchase #4 $211.49   12.188%   $237.2664   $237.27   $237.25   $237.30  
  Purchase #5 $13.65   4.199%   $14.2232   $14.22   $14.20   $14.20  
  Purchase #6 $79.39   8.146%   $85.8571   $85.86   $85.85   $85.90  
  Purchase #7 $246.64   7.553%   $265.2687   $265.27   $265.25   $265.30  
  7 purchase totals = $1,161.31       $1,265.5963   $1,265.60   $1,265.55   $1,265.60