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 $181.27   13.873%   $206.4176   $206.42   $206.40   $206.40  
  Purchase #2 $119.35   12.157%   $133.8594   $133.86   $133.85   $133.90  
  Purchase #3 $55.68   4.347%   $58.1004   $58.10   $58.10   $58.10  
  Purchase #4 $139.47   9.747%   $153.0641   $153.06   $153.05   $153.10  
  Purchase #5 $242.65   8.844%   $264.11   $264.11   $264.10   $264.10  
  Purchase #6 $16.58   7.700%   $17.8567   $17.86   $17.85   $17.90  
  Purchase #7 $52.62   3.750%   $54.5933   $54.59   $54.60   $54.60  
  7 purchase totals = $807.62       $888.0015   $888.00   $887.95   $888.10