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 $170.84   8.116%   $184.7054   $184.71   $184.70   $184.70  
  Purchase #2 $52.83   9.226%   $57.7041   $57.70   $57.70   $57.70  
  Purchase #3 $140.39   11.784%   $156.9336   $156.93   $156.95   $156.90  
  Purchase #4 $127.72   3.664%   $132.3997   $132.40   $132.40   $132.40  
  Purchase #5 $157.47   5.529%   $166.1765   $166.18   $166.20   $166.20  
  Purchase #6 $41.62   11.817%   $46.5382   $46.54   $46.55   $46.50  
  Purchase #7 $223.78   11.807%   $250.2017   $250.20   $250.20   $250.20  
  7 purchase totals = $914.65       $994.6592   $994.66   $994.70   $994.60