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 $163.67   8.122%   $176.9633   $176.96   $176.95   $177.00  
  Purchase #2 $82.95   11.138%   $92.189   $92.19   $92.20   $92.20  
  Purchase #3 $160.82   3.655%   $166.698   $166.70   $166.70   $166.70  
  Purchase #4 $212.99   4.228%   $221.9952   $222.00   $222.00   $222.00  
  Purchase #5 $44.42   4.835%   $46.5677   $46.57   $46.55   $46.60  
  Purchase #6 $80.35   8.676%   $87.3212   $87.32   $87.30   $87.30  
  Purchase #7 $175.37   5.784%   $185.5134   $185.51   $185.50   $185.50  
  7 purchase totals = $920.57       $977.2478   $977.25   $977.20   $977.30