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 $223.54   11.839%   $250.0049   $250.00   $250.00   $250.00  
  Purchase #2 $231.52   13.542%   $262.8724   $262.87   $262.85   $262.90  
  Purchase #3 $108.66   9.551%   $119.0381   $119.04   $119.05   $119.00  
  Purchase #4 $167.84   8.803%   $182.615   $182.62   $182.60   $182.60  
  Purchase #5 $102.52   3.127%   $105.7258   $105.73   $105.75   $105.70  
  Purchase #6 $236.94   8.684%   $257.5159   $257.52   $257.50   $257.50  
  Purchase #7 $169.81   12.322%   $190.734   $190.73   $190.75   $190.70  
  7 purchase totals = $1,240.83       $1,368.5061   $1,368.51   $1,368.50   $1,368.40