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 $243.58   13.797%   $277.1867   $277.19   $277.20   $277.20  
  Purchase #2 $92.47   5.132%   $97.2156   $97.22   $97.20   $97.20  
  Purchase #3 $117.48   9.599%   $128.7569   $128.76   $128.75   $128.80  
  Purchase #4 $111.86   4.767%   $117.1924   $117.19   $117.20   $117.20  
  Purchase #5 $240.51   4.588%   $251.5446   $251.54   $251.55   $251.50  
  Purchase #6 $151.30   11.535%   $168.7525   $168.75   $168.75   $168.80  
  Purchase #7 $145.54   12.408%   $163.5986   $163.60   $163.60   $163.60  
  7 purchase totals = $1,102.74       $1,204.2473   $1,204.25   $1,204.25   $1,204.30