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 $243.37   5.703%   $257.2494   $257.25   $257.25   $257.20  
  Purchase #2 $107.53   5.402%   $113.3388   $113.34   $113.35   $113.30  
  Purchase #3 $63.43   12.860%   $71.5871   $71.59   $71.60   $71.60  
  Purchase #4 $167.64   11.766%   $187.3645   $187.36   $187.35   $187.40  
  Purchase #5 $141.58   3.476%   $146.5013   $146.50   $146.50   $146.50  
  Purchase #6 $24.91   7.803%   $26.8537   $26.85   $26.85   $26.90  
  Purchase #7 $215.63   3.226%   $222.5862   $222.59   $222.60   $222.60  
  7 purchase totals = $964.09       $1,025.4810   $1,025.48   $1,025.50   $1,025.50