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 $212.43   8.528%   $230.546   $230.55   $230.55   $230.50  
  Purchase #2 $55.50   12.534%   $62.4564   $62.46   $62.45   $62.50  
  Purchase #3 $216.65   13.484%   $245.8631   $245.86   $245.85   $245.90  
  Purchase #4 $122.61   4.178%   $127.7326   $127.73   $127.75   $127.70  
  Purchase #5 $58.85   12.321%   $66.1009   $66.10   $66.10   $66.10  
  Purchase #6 $115.65   12.128%   $129.676   $129.68   $129.70   $129.70  
  Purchase #7 $135.37   9.807%   $148.6457   $148.65   $148.65   $148.60  
  7 purchase totals = $917.06       $1,011.0207   $1,011.03   $1,011.05   $1,011.00