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 $47.59   9.378%   $52.053   $52.05   $52.05   $52.10  
  Purchase #2 $45.85   10.571%   $50.6968   $50.70   $50.70   $50.70  
  Purchase #3 $130.49   4.653%   $136.5617   $136.56   $136.55   $136.60  
  Purchase #4 $153.76   6.196%   $163.287   $163.29   $163.30   $163.30  
  Purchase #5 $210.95   6.819%   $225.3347   $225.33   $225.35   $225.30  
  Purchase #6 $133.71   5.202%   $140.6656   $140.67   $140.65   $140.70  
  Purchase #7 $230.93   10.652%   $255.5287   $255.53   $255.55   $255.50  
  7 purchase totals = $953.28       $1,024.1275   $1,024.13   $1,024.15   $1,024.20