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 $55.97   12.522%   $62.9786   $62.98   $63.00   $63.00  
  Purchase #2 $37.66   10.273%   $41.5288   $41.53   $41.55   $41.50  
  Purchase #3 $246.48   7.695%   $265.4466   $265.45   $265.45   $265.40  
  Purchase #4 $89.76   8.156%   $97.0808   $97.08   $97.10   $97.10  
  Purchase #5 $89.96   10.841%   $99.7126   $99.71   $99.70   $99.70  
  Purchase #6 $202.72   5.755%   $214.3865   $214.39   $214.40   $214.40  
  Purchase #7 $76.97   6.427%   $81.9169   $81.92   $81.90   $81.90  
  7 purchase totals = $799.52       $863.0508   $863.06   $863.10   $863.00