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 $162.96   6.503%   $173.5573   $173.56   $173.55   $173.60  
  Purchase #2 $142.62   11.309%   $158.7489   $158.75   $158.75   $158.70  
  Purchase #3 $215.31   7.262%   $230.9458   $230.95   $230.95   $230.90  
  Purchase #4 $181.81   10.423%   $200.7601   $200.76   $200.75   $200.80  
  Purchase #5 $94.31   11.170%   $104.8444   $104.84   $104.85   $104.80  
  Purchase #6 $88.65   5.469%   $93.4983   $93.50   $93.50   $93.50  
  Purchase #7 $56.80   6.431%   $60.4528   $60.45   $60.45   $60.50  
  7 purchase totals = $942.46       $1,022.8076   $1,022.81   $1,022.80   $1,022.80