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 $84.46   11.642%   $94.2928   $94.29   $94.30   $94.30  
  Purchase #2 $188.36   6.407%   $200.4282   $200.43   $200.45   $200.40  
  Purchase #3 $150.61   13.495%   $170.9348   $170.93   $170.95   $170.90  
  Purchase #4 $41.51   8.546%   $45.0574   $45.06   $45.05   $45.10  
  Purchase #5 $150.31   11.768%   $167.9985   $168.00   $168.00   $168.00  
  Purchase #6 $157.75   3.499%   $163.2697   $163.27   $163.25   $163.30  
  Purchase #7 $105.26   9.129%   $114.8692   $114.87   $114.85   $114.90  
  7 purchase totals = $878.26       $956.8506   $956.85   $956.85   $956.90