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 $92.73   3.818%   $96.2704   $96.27   $96.25   $96.30  
  Purchase #2 $200.37   4.454%   $209.2945   $209.29   $209.30   $209.30  
  Purchase #3 $165.39   5.190%   $173.9737   $173.97   $173.95   $174.00  
  Purchase #4 $132.65   5.202%   $139.5505   $139.55   $139.55   $139.60  
  Purchase #5 $227.47   7.388%   $244.2755   $244.28   $244.30   $244.30  
  Purchase #6 $7.46   3.473%   $7.7191   $7.72   $7.70   $7.70  
  Purchase #7 $74.52   6.125%   $79.0844   $79.08   $79.10   $79.10  
  7 purchase totals = $900.59       $950.1681   $950.16   $950.15   $950.30