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 $95.75   9.493%   $104.8395   $104.84   $104.85   $104.80  
  Purchase #2 $122.56   6.336%   $130.3254   $130.33   $130.35   $130.30  
  Purchase #3 $85.42   8.748%   $92.8925   $92.89   $92.90   $92.90  
  Purchase #4 $199.37   5.233%   $209.803   $209.80   $209.80   $209.80  
  Purchase #5 $179.59   10.122%   $197.7681   $197.77   $197.75   $197.80  
  Purchase #6 $207.90   4.224%   $216.6817   $216.68   $216.70   $216.70  
  Purchase #7 $42.91   7.203%   $46.0008   $46.00   $46.00   $46.00  
  7 purchase totals = $933.50       $998.3110   $998.31   $998.35   $998.30