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 $123.70   6.827%   $132.145   $132.15   $132.15   $132.10  
  Purchase #2 $207.69   3.165%   $214.2634   $214.26   $214.25   $214.30  
  Purchase #3 $115.51   9.616%   $126.6174   $126.62   $126.60   $126.60  
  Purchase #4 $242.44   10.438%   $267.7459   $267.75   $267.75   $267.70  
  Purchase #5 $118.45   10.837%   $131.2864   $131.29   $131.30   $131.30  
  Purchase #6 $146.90   11.163%   $163.2984   $163.30   $163.30   $163.30  
  Purchase #7 $8.27   9.766%   $9.0776   $9.08   $9.10   $9.10  
  7 purchase totals = $962.96       $1,044.4341   $1,044.45   $1,044.45   $1,044.40