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 $237.65   12.568%   $267.5179   $267.52   $267.50   $267.50  
  Purchase #2 $117.67   7.851%   $126.9083   $126.91   $126.90   $126.90  
  Purchase #3 $234.88   12.126%   $263.3615   $263.36   $263.35   $263.40  
  Purchase #4 $95.87   5.413%   $101.0594   $101.06   $101.05   $101.10  
  Purchase #5 $189.56   4.667%   $198.4068   $198.41   $198.40   $198.40  
  Purchase #6 $32.85   6.838%   $35.0963   $35.10   $35.10   $35.10  
  Purchase #7 $179.57   12.775%   $202.5101   $202.51   $202.50   $202.50  
  7 purchase totals = $1,088.05       $1,194.8603   $1,194.87   $1,194.80   $1,194.90