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 $58.28   12.720%   $65.6932   $65.69   $65.70   $65.70  
  Purchase #2 $165.76   11.741%   $185.2219   $185.22   $185.20   $185.20  
  Purchase #3 $115.67   11.822%   $129.3445   $129.34   $129.35   $129.30  
  Purchase #4 $67.56   5.803%   $71.4805   $71.48   $71.50   $71.50  
  Purchase #5 $149.92   8.314%   $162.3843   $162.38   $162.40   $162.40  
  Purchase #6 $181.72   12.180%   $203.8535   $203.85   $203.85   $203.90  
  Purchase #7 $8.98   6.603%   $9.5729   $9.57   $9.55   $9.60  
  7 purchase totals = $747.89       $827.5508   $827.53   $827.55   $827.60