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 $59.91   11.256%   $66.6535   $66.65   $66.65   $66.70  
  Purchase #2 $58.28   4.404%   $60.8467   $60.85   $60.85   $60.80  
  Purchase #3 $85.44   13.497%   $96.9718   $96.97   $96.95   $97.00  
  Purchase #4 $35.34   12.823%   $39.8716   $39.87   $39.85   $39.90  
  Purchase #5 $180.87   13.265%   $204.8624   $204.86   $204.85   $204.90  
  Purchase #6 $227.70   3.490%   $235.6467   $235.65   $235.65   $235.60  
  Purchase #7 $144.50   5.613%   $152.6108   $152.61   $152.60   $152.60  
  7 purchase totals = $792.04       $857.4635   $857.46   $857.40   $857.50