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 $168.37   8.827%   $183.232   $183.23   $183.25   $183.20  
  Purchase #2 $224.34   9.581%   $245.834   $245.83   $245.85   $245.80  
  Purchase #3 $87.95   7.223%   $94.3026   $94.30   $94.30   $94.30  
  Purchase #4 $48.97   3.365%   $50.6178   $50.62   $50.60   $50.60  
  Purchase #5 $113.96   6.405%   $121.2591   $121.26   $121.25   $121.30  
  Purchase #6 $117.85   13.462%   $133.715   $133.72   $133.70   $133.70  
  Purchase #7 $81.66   4.753%   $85.5413   $85.54   $85.55   $85.50  
  7 purchase totals = $843.10       $914.5018   $914.50   $914.50   $914.40