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 $243.34   6.521%   $259.2082   $259.21   $259.20   $259.20  
  Purchase #2 $163.97   11.449%   $182.7429   $182.74   $182.75   $182.70  
  Purchase #3 $44.90   11.404%   $50.0204   $50.02   $50.00   $50.00  
  Purchase #4 $220.89   4.848%   $231.5987   $231.60   $231.60   $231.60  
  Purchase #5 $168.83   7.115%   $180.8423   $180.84   $180.85   $180.80  
  Purchase #6 $5.29   6.632%   $5.6408   $5.64   $5.65   $5.60  
  Purchase #7 $109.60   6.678%   $116.9191   $116.92   $116.90   $116.90  
  7 purchase totals = $956.82       $1,026.9724   $1,026.97   $1,026.95   $1,026.80