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 $124.70   5.448%   $131.4937   $131.49   $131.50   $131.50  
  Purchase #2 $31.67   4.691%   $33.1556   $33.16   $33.15   $33.20  
  Purchase #3 $97.66   6.556%   $104.0626   $104.06   $104.05   $104.10  
  Purchase #4 $24.77   5.637%   $26.1663   $26.17   $26.15   $26.20  
  Purchase #5 $199.74   7.102%   $213.9255   $213.93   $213.95   $213.90  
  Purchase #6 $182.59   9.821%   $200.5222   $200.52   $200.50   $200.50  
  Purchase #7 $217.50   8.819%   $236.6813   $236.68   $236.70   $236.70  
  7 purchase totals = $878.63       $946.0072   $946.01   $946.00   $946.10