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 $160.53   13.152%   $181.6429   $181.64   $181.65   $181.60  
  Purchase #2 $79.34   9.271%   $86.6956   $86.70   $86.70   $86.70  
  Purchase #3 $168.83   10.299%   $186.2178   $186.22   $186.20   $186.20  
  Purchase #4 $7.96   12.550%   $8.959   $8.96   $8.95   $9.00  
  Purchase #5 $179.84   6.245%   $191.071   $191.07   $191.05   $191.10  
  Purchase #6 $187.28   6.683%   $199.7959   $199.80   $199.80   $199.80  
  Purchase #7 $239.60   3.386%   $247.7129   $247.71   $247.70   $247.70  
  7 purchase totals = $1,023.38       $1,102.0951   $1,102.10   $1,102.05   $1,102.10