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 $198.85   4.268%   $207.3369   $207.34   $207.35   $207.30  
  Purchase #2 $23.95   9.371%   $26.1944   $26.19   $26.20   $26.20  
  Purchase #3 $220.25   13.238%   $249.4067   $249.41   $249.40   $249.40  
  Purchase #4 $139.27   12.519%   $156.7052   $156.71   $156.70   $156.70  
  Purchase #5 $181.52   11.302%   $202.0354   $202.04   $202.05   $202.00  
  Purchase #6 $169.80   6.253%   $180.4176   $180.42   $180.40   $180.40  
  Purchase #7 $207.50   12.768%   $233.9936   $233.99   $234.00   $234.00  
  7 purchase totals = $1,141.14       $1,256.0898   $1,256.10   $1,256.10   $1,256.00