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 $55.76   13.427%   $63.2469   $63.25   $63.25   $63.20  
  Purchase #2 $157.54   6.118%   $167.1783   $167.18   $167.20   $167.20  
  Purchase #3 $156.97   7.535%   $168.7977   $168.80   $168.80   $168.80  
  Purchase #4 $118.60   10.118%   $130.5999   $130.60   $130.60   $130.60  
  Purchase #5 $195.66   3.439%   $202.3887   $202.39   $202.40   $202.40  
  Purchase #6 $192.86   8.758%   $209.7507   $209.75   $209.75   $209.80  
  Purchase #7 $113.25   8.656%   $123.0529   $123.05   $123.05   $123.10  
  7 purchase totals = $990.64       $1,065.0151   $1,065.02   $1,065.05   $1,065.10