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 $168.73   11.216%   $187.6548   $187.65   $187.65   $187.70  
  Purchase #2 $40.42   10.126%   $44.5129   $44.51   $44.50   $44.50  
  Purchase #3 $80.77   10.412%   $89.1798   $89.18   $89.20   $89.20  
  Purchase #4 $136.51   12.215%   $153.1847   $153.18   $153.20   $153.20  
  Purchase #5 $196.49   3.705%   $203.77   $203.77   $203.75   $203.80  
  Purchase #6 $52.76   9.397%   $57.7179   $57.72   $57.70   $57.70  
  Purchase #7 $15.46   11.566%   $17.2481   $17.25   $17.25   $17.20  
  7 purchase totals = $691.14       $753.2682   $753.26   $753.25   $753.30