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 $208.54   11.693%   $232.9246   $232.92   $232.90   $232.90  
  Purchase #2 $111.59   7.569%   $120.0362   $120.04   $120.05   $120.00  
  Purchase #3 $218.50   12.137%   $245.0193   $245.02   $245.00   $245.00  
  Purchase #4 $17.95   6.188%   $19.0607   $19.06   $19.05   $19.10  
  Purchase #5 $240.97   12.271%   $270.5394   $270.54   $270.55   $270.50  
  Purchase #6 $11.90   4.597%   $12.447   $12.45   $12.45   $12.40  
  Purchase #7 $186.37   7.581%   $200.4987   $200.50   $200.50   $200.50  
  7 purchase totals = $995.82       $1,100.5259   $1,100.53   $1,100.50   $1,100.40