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 $201.47   7.362%   $216.3022   $216.30   $216.30   $216.30  
  Purchase #2 $165.79   8.462%   $179.8191   $179.82   $179.80   $179.80  
  Purchase #3 $14.54   12.513%   $16.3594   $16.36   $16.35   $16.40  
  Purchase #4 $145.47   5.835%   $153.9582   $153.96   $153.95   $154.00  
  Purchase #5 $178.62   4.260%   $186.2292   $186.23   $186.25   $186.20  
  Purchase #6 $16.31   3.446%   $16.872   $16.87   $16.85   $16.90  
  Purchase #7 $31.75   8.191%   $34.3506   $34.35   $34.35   $34.40  
  7 purchase totals = $753.95       $803.8907   $803.89   $803.85   $804.00