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 $119.29   13.432%   $135.313   $135.31   $135.30   $135.30  
  Purchase #2 $212.31   12.368%   $238.5685   $238.57   $238.55   $238.60  
  Purchase #3 $187.48   11.393%   $208.8396   $208.84   $208.85   $208.80  
  Purchase #4 $48.59   13.502%   $55.1506   $55.15   $55.15   $55.20  
  Purchase #5 $60.90   11.617%   $67.9748   $67.97   $67.95   $68.00  
  Purchase #6 $198.93   9.674%   $218.1745   $218.17   $218.15   $218.20  
  Purchase #7 $94.91   7.140%   $101.6866   $101.69   $101.70   $101.70  
  7 purchase totals = $922.41       $1,025.7076   $1,025.70   $1,025.65   $1,025.80