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 $64.77   13.835%   $73.7309   $73.73   $73.75   $73.70  
  Purchase #2 $32.39   8.495%   $35.1415   $35.14   $35.15   $35.10  
  Purchase #3 $236.57   3.523%   $244.9044   $244.90   $244.90   $244.90  
  Purchase #4 $147.50   12.366%   $165.7399   $165.74   $165.75   $165.70  
  Purchase #5 $156.79   12.680%   $176.671   $176.67   $176.65   $176.70  
  Purchase #6 $149.97   9.717%   $164.5426   $164.54   $164.55   $164.50  
  Purchase #7 $220.58   4.863%   $231.3068   $231.31   $231.30   $231.30  
  7 purchase totals = $1,008.57       $1,092.0371   $1,092.03   $1,092.05   $1,091.90