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 $61.62   7.454%   $66.2132   $66.21   $66.20   $66.20  
  Purchase #2 $187.69   10.634%   $207.649   $207.65   $207.65   $207.60  
  Purchase #3 $213.40   9.722%   $234.1467   $234.15   $234.15   $234.10  
  Purchase #4 $229.60   12.307%   $257.8569   $257.86   $257.85   $257.90  
  Purchase #5 $240.87   13.706%   $273.8836   $273.88   $273.90   $273.90  
  Purchase #6 $138.89   3.773%   $144.1303   $144.13   $144.15   $144.10  
  Purchase #7 $222.74   11.626%   $248.6358   $248.64   $248.65   $248.60  
  7 purchase totals = $1,294.81       $1,432.5155   $1,432.52   $1,432.55   $1,432.40