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 $187.29   9.322%   $204.7492   $204.75   $204.75   $204.70  
  Purchase #2 $222.33   8.651%   $241.5638   $241.56   $241.55   $241.60  
  Purchase #3 $64.63   3.455%   $66.863   $66.86   $66.85   $66.90  
  Purchase #4 $184.89   10.597%   $204.4828   $204.48   $204.50   $204.50  
  Purchase #5 $91.77   4.258%   $95.6776   $95.68   $95.70   $95.70  
  Purchase #6 $60.87   6.506%   $64.8302   $64.83   $64.85   $64.80  
  Purchase #7 $215.26   12.261%   $241.653   $241.65   $241.65   $241.70  
  7 purchase totals = $1,027.04       $1,119.8196   $1,119.81   $1,119.85   $1,119.90