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 $57.67   6.738%   $61.5558   $61.56   $61.55   $61.60  
  Purchase #2 $139.48   10.484%   $154.1031   $154.10   $154.10   $154.10  
  Purchase #3 $189.42   5.854%   $200.5086   $200.51   $200.50   $200.50  
  Purchase #4 $178.99   5.144%   $188.1972   $188.20   $188.20   $188.20  
  Purchase #5 $60.50   7.616%   $65.1077   $65.11   $65.10   $65.10  
  Purchase #6 $97.53   12.823%   $110.0363   $110.04   $110.05   $110.00  
  Purchase #7 $242.97   9.535%   $266.1372   $266.14   $266.15   $266.10  
  7 purchase totals = $966.56       $1,045.6459   $1,045.66   $1,045.65   $1,045.60