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 $182.67   10.601%   $202.0348   $202.03   $202.05   $202.00  
  Purchase #2 $68.95   7.256%   $73.953   $73.95   $73.95   $74.00  
  Purchase #3 $126.91   8.751%   $138.0159   $138.02   $138.00   $138.00  
  Purchase #4 $128.77   3.649%   $133.4688   $133.47   $133.45   $133.50  
  Purchase #5 $233.56   6.648%   $249.0871   $249.09   $249.10   $249.10  
  Purchase #6 $16.83   6.228%   $17.8782   $17.88   $17.90   $17.90  
  Purchase #7 $174.67   9.851%   $191.8767   $191.88   $191.90   $191.90  
  7 purchase totals = $932.36       $1,006.3145   $1,006.32   $1,006.35   $1,006.40