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 $219.82   12.661%   $247.6514   $247.65   $247.65   $247.70  
  Purchase #2 $64.89   11.342%   $72.2498   $72.25   $72.25   $72.20  
  Purchase #3 $97.67   13.643%   $110.9951   $111.00   $111.00   $111.00  
  Purchase #4 $66.82   9.851%   $73.4024   $73.40   $73.40   $73.40  
  Purchase #5 $167.64   8.429%   $181.7704   $181.77   $181.75   $181.80  
  Purchase #6 $182.86   6.771%   $195.2415   $195.24   $195.25   $195.20  
  Purchase #7 $164.99   8.542%   $179.0834   $179.08   $179.10   $179.10  
  7 purchase totals = $964.69       $1,060.3940   $1,060.39   $1,060.40   $1,060.40