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 $225.60   9.462%   $246.9463   $246.95   $246.95   $246.90  
  Purchase #2 $215.40   11.118%   $239.3482   $239.35   $239.35   $239.30  
  Purchase #3 $20.36   12.411%   $22.8869   $22.89   $22.90   $22.90  
  Purchase #4 $232.59   7.745%   $250.6041   $250.60   $250.60   $250.60  
  Purchase #5 $122.94   6.321%   $130.711   $130.71   $130.70   $130.70  
  Purchase #6 $97.81   10.824%   $108.397   $108.40   $108.40   $108.40  
  Purchase #7 $150.56   7.524%   $161.8881   $161.89   $161.90   $161.90  
  7 purchase totals = $1,065.26       $1,160.7816   $1,160.79   $1,160.80   $1,160.70