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 $71.97   6.453%   $76.6142   $76.61   $76.60   $76.60  
  Purchase #2 $87.34   10.368%   $96.3954   $96.40   $96.40   $96.40  
  Purchase #3 $24.60   3.801%   $25.535   $25.54   $25.55   $25.50  
  Purchase #4 $19.60   13.310%   $22.2088   $22.21   $22.20   $22.20  
  Purchase #5 $14.50   12.728%   $16.3456   $16.35   $16.35   $16.30  
  Purchase #6 $6.62   13.629%   $7.5222   $7.52   $7.50   $7.50  
  Purchase #7 $232.84   6.469%   $247.9024   $247.90   $247.90   $247.90  
  7 purchase totals = $457.47       $492.5236   $492.53   $492.50   $492.40