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 $241.93   10.721%   $267.8673   $267.87   $267.85   $267.90  
  Purchase #2 $68.68   10.717%   $76.0404   $76.04   $76.05   $76.00  
  Purchase #3 $235.32   12.638%   $265.0597   $265.06   $265.05   $265.10  
  Purchase #4 $237.78   3.419%   $245.9097   $245.91   $245.90   $245.90  
  Purchase #5 $225.37   9.834%   $247.5329   $247.53   $247.55   $247.50  
  Purchase #6 $93.46   4.830%   $97.9741   $97.97   $97.95   $98.00  
  Purchase #7 $67.63   6.796%   $72.2261   $72.23   $72.25   $72.20  
  7 purchase totals = $1,170.17       $1,272.6102   $1,272.61   $1,272.60   $1,272.60