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 $180.77   11.871%   $202.2292   $202.23   $202.25   $202.20  
  Purchase #2 $116.83   6.734%   $124.6973   $124.70   $124.70   $124.70  
  Purchase #3 $205.32   5.413%   $216.434   $216.43   $216.45   $216.40  
  Purchase #4 $106.47   12.285%   $119.5498   $119.55   $119.55   $119.50  
  Purchase #5 $169.57   13.426%   $192.3365   $192.34   $192.35   $192.30  
  Purchase #6 $244.64   11.777%   $273.4513   $273.45   $273.45   $273.50  
  Purchase #7 $20.94   3.484%   $21.6695   $21.67   $21.65   $21.70  
  7 purchase totals = $1,044.54       $1,150.3676   $1,150.37   $1,150.40   $1,150.30