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 $194.99   7.731%   $210.0647   $210.06   $210.05   $210.10  
  Purchase #2 $172.42   12.113%   $193.3052   $193.31   $193.30   $193.30  
  Purchase #3 $23.68   3.595%   $24.5313   $24.53   $24.55   $24.50  
  Purchase #4 $156.64   7.198%   $167.9149   $167.91   $167.90   $167.90  
  Purchase #5 $68.32   6.796%   $72.963   $72.96   $72.95   $73.00  
  Purchase #6 $191.53   10.493%   $211.6272   $211.63   $211.65   $211.60  
  Purchase #7 $118.81   5.792%   $125.6915   $125.69   $125.70   $125.70  
  7 purchase totals = $926.39       $1,006.0978   $1,006.09   $1,006.10   $1,006.10