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 $21.55   11.624%   $24.055   $24.06   $24.05   $24.10  
  Purchase #2 $179.87   7.135%   $192.7037   $192.70   $192.70   $192.70  
  Purchase #3 $170.78   13.226%   $193.3674   $193.37   $193.35   $193.40  
  Purchase #4 $82.78   5.448%   $87.2899   $87.29   $87.30   $87.30  
  Purchase #5 $212.74   6.271%   $226.0809   $226.08   $226.10   $226.10  
  Purchase #6 $98.31   11.103%   $109.2254   $109.23   $109.25   $109.20  
  Purchase #7 $226.65   9.507%   $248.1976   $248.20   $248.20   $248.20  
  7 purchase totals = $992.68       $1,080.9199   $1,080.93   $1,080.95   $1,081.00