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 $59.29   12.546%   $66.7285   $66.73   $66.75   $66.70  
  Purchase #2 $64.48   8.182%   $69.7558   $69.76   $69.75   $69.80  
  Purchase #3 $122.92   5.539%   $129.7285   $129.73   $129.75   $129.70  
  Purchase #4 $163.83   5.146%   $172.2607   $172.26   $172.25   $172.30  
  Purchase #5 $58.52   4.376%   $61.0808   $61.08   $61.10   $61.10  
  Purchase #6 $190.61   3.566%   $197.4072   $197.41   $197.40   $197.40  
  Purchase #7 $91.60   4.458%   $95.6835   $95.68   $95.70   $95.70  
  7 purchase totals = $751.25       $792.6450   $792.65   $792.70   $792.70