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 $209.41   6.492%   $223.0049   $223.00   $223.00   $223.00  
  Purchase #2 $236.67   13.214%   $267.9436   $267.94   $267.95   $267.90  
  Purchase #3 $242.92   12.734%   $273.8534   $273.85   $273.85   $273.90  
  Purchase #4 $28.74   10.356%   $31.7163   $31.72   $31.70   $31.70  
  Purchase #5 $33.98   12.395%   $38.1918   $38.19   $38.20   $38.20  
  Purchase #6 $169.54   6.221%   $180.0871   $180.09   $180.10   $180.10  
  Purchase #7 $224.90   3.601%   $232.9986   $233.00   $233.00   $233.00  
  7 purchase totals = $1,146.16       $1,247.7957   $1,247.79   $1,247.80   $1,247.80