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 $248.84   13.688%   $282.9012   $282.90   $282.90   $282.90  
  Purchase #2 $97.96   7.390%   $105.1992   $105.20   $105.20   $105.20  
  Purchase #3 $161.27   3.403%   $166.758   $166.76   $166.75   $166.80  
  Purchase #4 $246.57   8.682%   $267.9772   $267.98   $268.00   $268.00  
  Purchase #5 $249.92   3.837%   $259.5094   $259.51   $259.50   $259.50  
  Purchase #6 $124.63   11.272%   $138.6783   $138.68   $138.70   $138.70  
  Purchase #7 $21.33   10.278%   $23.5223   $23.52   $23.50   $23.50  
  7 purchase totals = $1,150.52       $1,244.5456   $1,244.55   $1,244.55   $1,244.60