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 $57.60   13.814%   $65.5569   $65.56   $65.55   $65.60  
  Purchase #2 $220.71   6.729%   $235.5616   $235.56   $235.55   $235.60  
  Purchase #3 $156.85   5.635%   $165.6885   $165.69   $165.70   $165.70  
  Purchase #4 $170.28   4.824%   $178.4943   $178.49   $178.50   $178.50  
  Purchase #5 $249.92   10.204%   $275.4218   $275.42   $275.40   $275.40  
  Purchase #6 $182.29   5.205%   $191.7782   $191.78   $191.80   $191.80  
  Purchase #7 $116.62   8.212%   $126.1968   $126.20   $126.20   $126.20  
  7 purchase totals = $1,154.27       $1,238.6981   $1,238.70   $1,238.70   $1,238.80