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 $64.41   6.487%   $68.5883   $68.59   $68.60   $68.60  
  Purchase #2 $231.37   10.872%   $256.5245   $256.52   $256.50   $256.50  
  Purchase #3 $55.37   6.386%   $58.9059   $58.91   $58.90   $58.90  
  Purchase #4 $105.70   7.722%   $113.8622   $113.86   $113.85   $113.90  
  Purchase #5 $84.68   10.387%   $93.4757   $93.48   $93.50   $93.50  
  Purchase #6 $214.35   7.715%   $230.8871   $230.89   $230.90   $230.90  
  Purchase #7 $230.51   11.188%   $256.2995   $256.30   $256.30   $256.30  
  7 purchase totals = $986.39       $1,078.5432   $1,078.55   $1,078.55   $1,078.60