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 $208.27   13.349%   $236.072   $236.07   $236.05   $236.10  
  Purchase #2 $29.99   6.118%   $31.8248   $31.82   $31.80   $31.80  
  Purchase #3 $85.75   3.676%   $88.9022   $88.90   $88.90   $88.90  
  Purchase #4 $244.82   8.647%   $265.9896   $265.99   $266.00   $266.00  
  Purchase #5 $165.40   13.767%   $188.1706   $188.17   $188.15   $188.20  
  Purchase #6 $165.88   7.323%   $178.0274   $178.03   $178.05   $178.00  
  Purchase #7 $157.33   3.420%   $162.7107   $162.71   $162.70   $162.70  
  7 purchase totals = $1,057.44       $1,151.6973   $1,151.69   $1,151.65   $1,151.70