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 $204.66   7.631%   $220.2776   $220.28   $220.30   $220.30  
  Purchase #2 $96.32   6.294%   $102.3824   $102.38   $102.40   $102.40  
  Purchase #3 $119.31   10.508%   $131.8471   $131.85   $131.85   $131.80  
  Purchase #4 $199.42   8.403%   $216.1773   $216.18   $216.20   $216.20  
  Purchase #5 $222.73   7.260%   $238.9002   $238.90   $238.90   $238.90  
  Purchase #6 $199.76   5.244%   $210.2354   $210.24   $210.25   $210.20  
  Purchase #7 $223.96   4.419%   $233.8568   $233.86   $233.85   $233.90  
  7 purchase totals = $1,266.16       $1,353.6768   $1,353.69   $1,353.75   $1,353.70