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 $131.96   13.604%   $149.9118   $149.91   $149.90   $149.90  
  Purchase #2 $229.28   11.257%   $255.09   $255.09   $255.10   $255.10  
  Purchase #3 $95.28   13.817%   $108.4448   $108.44   $108.45   $108.40  
  Purchase #4 $176.28   13.390%   $199.8839   $199.88   $199.90   $199.90  
  Purchase #5 $27.67   4.194%   $28.8305   $28.83   $28.85   $28.80  
  Purchase #6 $158.35   10.281%   $174.63   $174.63   $174.65   $174.60  
  Purchase #7 $210.83   9.864%   $231.6263   $231.63   $231.65   $231.60  
  7 purchase totals = $1,029.65       $1,148.4173   $1,148.41   $1,148.50   $1,148.30