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 $59.95   3.535%   $62.0692   $62.07   $62.05   $62.10  
  Purchase #2 $199.45   8.451%   $216.3055   $216.31   $216.30   $216.30  
  Purchase #3 $85.33   7.241%   $91.5087   $91.51   $91.50   $91.50  
  Purchase #4 $59.32   4.156%   $61.7853   $61.79   $61.80   $61.80  
  Purchase #5 $248.68   5.209%   $261.6337   $261.63   $261.65   $261.60  
  Purchase #6 $80.82   3.317%   $83.5008   $83.50   $83.50   $83.50  
  Purchase #7 $160.91   5.829%   $170.2894   $170.29   $170.30   $170.30  
  7 purchase totals = $894.46       $947.0926   $947.10   $947.10   $947.10