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 $211.87   8.632%   $230.1586   $230.16   $230.15   $230.20  
  Purchase #2 $37.64   5.542%   $39.726   $39.73   $39.75   $39.70  
  Purchase #3 $41.51   13.433%   $47.086   $47.09   $47.10   $47.10  
  Purchase #4 $154.77   10.827%   $171.5269   $171.53   $171.55   $171.50  
  Purchase #5 $18.52   10.791%   $20.5185   $20.52   $20.50   $20.50  
  Purchase #6 $56.98   8.406%   $61.7697   $61.77   $61.75   $61.80  
  Purchase #7 $195.26   5.492%   $205.9837   $205.98   $206.00   $206.00  
  7 purchase totals = $716.55       $776.7694   $776.78   $776.80   $776.80