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 $119.55   13.204%   $135.3354   $135.34   $135.35   $135.30  
  Purchase #2 $159.44   7.687%   $171.6962   $171.70   $171.70   $171.70  
  Purchase #3 $165.58   6.593%   $176.4967   $176.50   $176.50   $176.50  
  Purchase #4 $228.53   3.534%   $236.6063   $236.61   $236.60   $236.60  
  Purchase #5 $238.69   11.705%   $266.6287   $266.63   $266.65   $266.60  
  Purchase #6 $193.91   4.739%   $203.0994   $203.10   $203.10   $203.10  
  Purchase #7 $189.44   11.386%   $211.0096   $211.01   $211.00   $211.00  
  7 purchase totals = $1,295.14       $1,400.8723   $1,400.89   $1,400.90   $1,400.80