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 $85.73   13.212%   $97.0566   $97.06   $97.05   $97.10  
  Purchase #2 $220.26   6.544%   $234.6738   $234.67   $234.65   $234.70  
  Purchase #3 $221.77   6.688%   $236.602   $236.60   $236.60   $236.60  
  Purchase #4 $229.86   6.151%   $243.9987   $244.00   $244.00   $244.00  
  Purchase #5 $236.50   13.660%   $268.8059   $268.81   $268.80   $268.80  
  Purchase #6 $113.96   13.843%   $129.7355   $129.74   $129.75   $129.70  
  Purchase #7 $135.60   12.247%   $152.2069   $152.21   $152.20   $152.20  
  7 purchase totals = $1,243.68       $1,363.0794   $1,363.09   $1,363.05   $1,363.10