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 $202.70   11.418%   $225.8443   $225.84   $225.85   $225.80  
  Purchase #2 $53.91   11.396%   $60.0536   $60.05   $60.05   $60.10  
  Purchase #3 $238.38   8.849%   $259.4742   $259.47   $259.45   $259.50  
  Purchase #4 $68.57   5.170%   $72.1151   $72.12   $72.10   $72.10  
  Purchase #5 $63.53   4.678%   $66.5019   $66.50   $66.50   $66.50  
  Purchase #6 $178.86   7.235%   $191.8005   $191.80   $191.80   $191.80  
  Purchase #7 $175.32   10.754%   $194.1739   $194.17   $194.15   $194.20  
  7 purchase totals = $981.27       $1,069.9635   $1,069.95   $1,069.90   $1,070.00