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 $222.82   8.492%   $241.7419   $241.74   $241.75   $241.70  
  Purchase #2 $209.66   10.547%   $231.7728   $231.77   $231.75   $231.80  
  Purchase #3 $124.53   4.609%   $130.2696   $130.27   $130.25   $130.30  
  Purchase #4 $18.29   4.179%   $19.0543   $19.05   $19.05   $19.10  
  Purchase #5 $146.39   5.323%   $154.1823   $154.18   $154.20   $154.20  
  Purchase #6 $194.36   3.737%   $201.6232   $201.62   $201.60   $201.60  
  Purchase #7 $163.79   6.395%   $174.2644   $174.26   $174.25   $174.30  
  7 purchase totals = $1,079.84       $1,152.9085   $1,152.89   $1,152.85   $1,153.00