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 $90.93   4.590%   $95.1037   $95.10   $95.10   $95.10  
  Purchase #2 $224.62   7.123%   $240.6197   $240.62   $240.60   $240.60  
  Purchase #3 $151.69   10.417%   $167.4915   $167.49   $167.50   $167.50  
  Purchase #4 $84.46   11.533%   $94.2008   $94.20   $94.20   $94.20  
  Purchase #5 $207.39   11.753%   $231.7645   $231.76   $231.75   $231.80  
  Purchase #6 $164.77   13.454%   $186.9382   $186.94   $186.95   $186.90  
  Purchase #7 $15.90   12.620%   $17.9066   $17.91   $17.90   $17.90  
  7 purchase totals = $939.76       $1,034.0250   $1,034.02   $1,034.00   $1,034.00