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 $202.73   10.527%   $224.0714   $224.07   $224.05   $224.10  
  Purchase #2 $77.83   10.658%   $86.1251   $86.13   $86.15   $86.10  
  Purchase #3 $104.55   8.104%   $113.0227   $113.02   $113.00   $113.00  
  Purchase #4 $164.54   12.792%   $185.588   $185.59   $185.60   $185.60  
  Purchase #5 $73.87   11.811%   $82.5948   $82.59   $82.60   $82.60  
  Purchase #6 $161.80   12.281%   $181.6707   $181.67   $181.65   $181.70  
  Purchase #7 $69.79   10.299%   $76.9777   $76.98   $77.00   $77.00  
  7 purchase totals = $855.11       $950.0504   $950.05   $950.05   $950.10