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 $203.93   8.590%   $221.4476   $221.45   $221.45   $221.40  
  Purchase #2 $173.41   10.587%   $191.7689   $191.77   $191.75   $191.80  
  Purchase #3 $23.67   12.414%   $26.6084   $26.61   $26.60   $26.60  
  Purchase #4 $200.35   10.604%   $221.5951   $221.60   $221.60   $221.60  
  Purchase #5 $159.29   3.357%   $164.6374   $164.64   $164.65   $164.60  
  Purchase #6 $120.66   12.503%   $135.7461   $135.75   $135.75   $135.70  
  Purchase #7 $101.25   11.719%   $113.1155   $113.12   $113.10   $113.10  
  7 purchase totals = $982.56       $1,074.9190   $1,074.94   $1,074.90   $1,074.80