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 $62.41   13.106%   $70.5895   $70.59   $70.60   $70.60  
  Purchase #2 $116.49   8.664%   $126.5827   $126.58   $126.60   $126.60  
  Purchase #3 $72.76   8.465%   $78.9191   $78.92   $78.90   $78.90  
  Purchase #4 $199.35   5.118%   $209.5527   $209.55   $209.55   $209.60  
  Purchase #5 $214.57   11.472%   $239.1855   $239.19   $239.20   $239.20  
  Purchase #6 $194.52   9.717%   $213.4215   $213.42   $213.40   $213.40  
  Purchase #7 $238.67   4.824%   $250.1834   $250.18   $250.20   $250.20  
  7 purchase totals = $1,098.77       $1,188.4344   $1,188.43   $1,188.45   $1,188.50