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 $67.48   10.242%   $74.3913   $74.39   $74.40   $74.40  
  Purchase #2 $137.84   12.132%   $154.5627   $154.56   $154.55   $154.60  
  Purchase #3 $117.25   4.108%   $122.0666   $122.07   $122.05   $122.10  
  Purchase #4 $186.81   13.492%   $212.0144   $212.01   $212.00   $212.00  
  Purchase #5 $172.98   8.203%   $187.1695   $187.17   $187.15   $187.20  
  Purchase #6 $57.96   12.824%   $65.3928   $65.39   $65.40   $65.40  
  Purchase #7 $190.77   8.212%   $206.436   $206.44   $206.45   $206.40  
  7 purchase totals = $931.09       $1,022.0333   $1,022.03   $1,022.00   $1,022.10