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 $146.96   6.298%   $156.2155   $156.22   $156.20   $156.20  
  Purchase #2 $186.57   9.640%   $204.5553   $204.56   $204.55   $204.60  
  Purchase #3 $168.47   11.360%   $187.6082   $187.61   $187.60   $187.60  
  Purchase #4 $207.68   10.299%   $229.069   $229.07   $229.05   $229.10  
  Purchase #5 $26.72   7.430%   $28.7053   $28.71   $28.70   $28.70  
  Purchase #6 $235.47   7.505%   $253.142   $253.14   $253.15   $253.10  
  Purchase #7 $94.45   4.152%   $98.3716   $98.37   $98.35   $98.40  
  7 purchase totals = $1,066.32       $1,157.6669   $1,157.68   $1,157.60   $1,157.70