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 $202.93   12.831%   $228.9679   $228.97   $228.95   $229.00  
  Purchase #2 $33.45   11.708%   $37.3663   $37.37   $37.35   $37.40  
  Purchase #3 $62.95   13.512%   $71.4558   $71.46   $71.45   $71.50  
  Purchase #4 $65.97   3.259%   $68.12   $68.12   $68.10   $68.10  
  Purchase #5 $165.89   3.446%   $171.6066   $171.61   $171.60   $171.60  
  Purchase #6 $168.68   10.677%   $186.69   $186.69   $186.70   $186.70  
  Purchase #7 $164.78   12.508%   $185.3907   $185.39   $185.40   $185.40  
  7 purchase totals = $864.65       $949.5973   $949.61   $949.55   $949.70