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 $78.96   6.751%   $84.2906   $84.29   $84.30   $84.30  
  Purchase #2 $177.74   3.531%   $184.016   $184.02   $184.00   $184.00  
  Purchase #3 $67.60   10.197%   $74.4932   $74.49   $74.50   $74.50  
  Purchase #4 $82.55   6.286%   $87.7391   $87.74   $87.75   $87.70  
  Purchase #5 $245.47   3.174%   $253.2612   $253.26   $253.25   $253.30  
  Purchase #6 $45.89   6.580%   $48.9096   $48.91   $48.90   $48.90  
  Purchase #7 $200.66   7.632%   $215.9744   $215.97   $215.95   $216.00  
  7 purchase totals = $898.87       $948.6841   $948.68   $948.65   $948.70