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 $223.76   7.687%   $240.9604   $240.96   $240.95   $241.00  
  Purchase #2 $138.51   7.542%   $148.9564   $148.96   $148.95   $149.00  
  Purchase #3 $64.37   13.831%   $73.273   $73.27   $73.25   $73.30  
  Purchase #4 $175.79   7.265%   $188.5611   $188.56   $188.55   $188.60  
  Purchase #5 $54.62   12.681%   $61.5464   $61.55   $61.55   $61.50  
  Purchase #6 $136.83   5.243%   $144.004   $144.00   $144.00   $144.00  
  Purchase #7 $134.29   9.267%   $146.7347   $146.73   $146.75   $146.70  
  7 purchase totals = $928.17       $1,004.0360   $1,004.03   $1,004.00   $1,004.10