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 $214.78   8.126%   $232.233   $232.23   $232.25   $232.20  
  Purchase #2 $237.74   12.283%   $266.9416   $266.94   $266.95   $266.90  
  Purchase #3 $53.50   8.405%   $57.9967   $58.00   $58.00   $58.00  
  Purchase #4 $25.43   10.202%   $28.0244   $28.02   $28.00   $28.00  
  Purchase #5 $128.28   13.453%   $145.5375   $145.54   $145.55   $145.50  
  Purchase #6 $188.41   9.558%   $206.4182   $206.42   $206.40   $206.40  
  Purchase #7 $242.86   5.348%   $255.8482   $255.85   $255.85   $255.80  
  7 purchase totals = $1,091.00       $1,192.9996   $1,193.00   $1,193.00   $1,192.80