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 $100.28   12.334%   $112.6485   $112.65   $112.65   $112.60  
  Purchase #2 $177.84   5.834%   $188.2152   $188.22   $188.20   $188.20  
  Purchase #3 $56.99   4.746%   $59.6947   $59.69   $59.70   $59.70  
  Purchase #4 $219.54   11.710%   $245.2481   $245.25   $245.25   $245.20  
  Purchase #5 $153.95   9.689%   $168.8662   $168.87   $168.85   $168.90  
  Purchase #6 $160.31   10.321%   $176.8556   $176.86   $176.85   $176.90  
  Purchase #7 $97.25   5.634%   $102.7291   $102.73   $102.75   $102.70  
  7 purchase totals = $966.16       $1,054.2574   $1,054.27   $1,054.25   $1,054.20