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 $232.96   11.284%   $259.2472   $259.25   $259.25   $259.20  
  Purchase #2 $153.30   6.808%   $163.7367   $163.74   $163.75   $163.70  
  Purchase #3 $66.92   7.535%   $71.9624   $71.96   $71.95   $72.00  
  Purchase #4 $158.54   10.607%   $175.3563   $175.36   $175.35   $175.40  
  Purchase #5 $53.31   9.384%   $58.3126   $58.31   $58.30   $58.30  
  Purchase #6 $74.88   12.504%   $84.243   $84.24   $84.25   $84.20  
  Purchase #7 $225.85   9.632%   $247.6039   $247.60   $247.60   $247.60  
  7 purchase totals = $965.76       $1,060.4621   $1,060.46   $1,060.45   $1,060.40