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 $216.66   9.716%   $237.7107   $237.71   $237.70   $237.70  
  Purchase #2 $235.54   9.524%   $257.9728   $257.97   $257.95   $258.00  
  Purchase #3 $15.74   11.666%   $17.5762   $17.58   $17.60   $17.60  
  Purchase #4 $234.91   13.607%   $266.8742   $266.87   $266.85   $266.90  
  Purchase #5 $232.38   5.210%   $244.487   $244.49   $244.50   $244.50  
  Purchase #6 $183.57   5.596%   $193.8426   $193.84   $193.85   $193.80  
  Purchase #7 $48.26   5.475%   $50.9022   $50.90   $50.90   $50.90  
  7 purchase totals = $1,167.06       $1,269.3657   $1,269.36   $1,269.35   $1,269.40