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 $42.56   12.253%   $47.7749   $47.77   $47.75   $47.80  
  Purchase #2 $156.37   7.210%   $167.6443   $167.64   $167.65   $167.60  
  Purchase #3 $14.65   12.815%   $16.5274   $16.53   $16.55   $16.50  
  Purchase #4 $226.84   5.565%   $239.4636   $239.46   $239.45   $239.50  
  Purchase #5 $191.36   7.158%   $205.0575   $205.06   $205.05   $205.10  
  Purchase #6 $201.96   3.845%   $209.7254   $209.73   $209.75   $209.70  
  Purchase #7 $130.26   9.816%   $143.0463   $143.05   $143.05   $143.00  
  7 purchase totals = $964.00       $1,029.2394   $1,029.24   $1,029.25   $1,029.20