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 $238.89   10.722%   $264.5038   $264.50   $264.50   $264.50  
  Purchase #2 $58.71   11.817%   $65.6478   $65.65   $65.65   $65.60  
  Purchase #3 $66.57   3.532%   $68.9213   $68.92   $68.90   $68.90  
  Purchase #4 $198.43   4.665%   $207.6868   $207.69   $207.70   $207.70  
  Purchase #5 $195.48   10.528%   $216.0601   $216.06   $216.05   $216.10  
  Purchase #6 $91.92   5.673%   $97.1346   $97.13   $97.15   $97.10  
  Purchase #7 $187.82   11.384%   $209.2014   $209.20   $209.20   $209.20  
  7 purchase totals = $1,037.82       $1,129.1558   $1,129.15   $1,129.15   $1,129.10