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 $125.48   6.598%   $133.7592   $133.76   $133.75   $133.80  
  Purchase #2 $119.29   13.374%   $135.2438   $135.24   $135.25   $135.20  
  Purchase #3 $82.65   7.655%   $88.9769   $88.98   $89.00   $89.00  
  Purchase #4 $194.45   3.485%   $201.2266   $201.23   $201.25   $201.20  
  Purchase #5 $218.63   13.269%   $247.64   $247.64   $247.65   $247.60  
  Purchase #6 $241.72   12.774%   $272.5973   $272.60   $272.60   $272.60  
  Purchase #7 $124.40   8.769%   $135.3086   $135.31   $135.30   $135.30  
  7 purchase totals = $1,106.62       $1,214.7524   $1,214.76   $1,214.80   $1,214.70