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 $197.80   6.796%   $211.2425   $211.24   $211.25   $211.20  
  Purchase #2 $62.84   5.194%   $66.1039   $66.10   $66.10   $66.10  
  Purchase #3 $174.34   7.577%   $187.5497   $187.55   $187.55   $187.50  
  Purchase #4 $106.68   7.611%   $114.7994   $114.80   $114.80   $114.80  
  Purchase #5 $182.75   11.650%   $204.0404   $204.04   $204.05   $204.00  
  Purchase #6 $91.47   6.667%   $97.5683   $97.57   $97.55   $97.60  
  Purchase #7 $134.92   6.242%   $143.3417   $143.34   $143.35   $143.30  
  7 purchase totals = $950.80       $1,024.6459   $1,024.64   $1,024.65   $1,024.50