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 $38.48   8.437%   $41.7266   $41.73   $41.75   $41.70  
  Purchase #2 $123.70   5.860%   $130.9488   $130.95   $130.95   $130.90  
  Purchase #3 $65.98   9.420%   $72.1953   $72.20   $72.20   $72.20  
  Purchase #4 $238.26   12.482%   $267.9996   $268.00   $268.00   $268.00  
  Purchase #5 $166.66   9.230%   $182.0427   $182.04   $182.05   $182.00  
  Purchase #6 $246.57   9.194%   $269.2396   $269.24   $269.25   $269.20  
  Purchase #7 $99.82   5.263%   $105.0735   $105.07   $105.05   $105.10  
  7 purchase totals = $979.47       $1,069.2261   $1,069.23   $1,069.25   $1,069.10