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 $223.29   11.435%   $248.8232   $248.82   $248.80   $248.80  
  Purchase #2 $38.85   6.124%   $41.2292   $41.23   $41.25   $41.20  
  Purchase #3 $128.36   8.706%   $139.535   $139.54   $139.55   $139.50  
  Purchase #4 $25.80   4.708%   $27.0147   $27.01   $27.00   $27.00  
  Purchase #5 $188.69   10.478%   $208.4609   $208.46   $208.45   $208.50  
  Purchase #6 $174.69   6.511%   $186.0641   $186.06   $186.05   $186.10  
  Purchase #7 $111.65   11.219%   $124.176   $124.18   $124.20   $124.20  
  7 purchase totals = $891.33       $975.3031   $975.30   $975.30   $975.30