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 $65.69   12.145%   $73.6681   $73.67   $73.65   $73.70  
  Purchase #2 $83.81   10.158%   $92.3234   $92.32   $92.30   $92.30  
  Purchase #3 $60.62   4.869%   $63.5716   $63.57   $63.55   $63.60  
  Purchase #4 $145.43   8.824%   $158.2627   $158.26   $158.25   $158.30  
  Purchase #5 $211.80   6.132%   $224.7876   $224.79   $224.80   $224.80  
  Purchase #6 $184.58   12.686%   $207.9958   $208.00   $208.00   $208.00  
  Purchase #7 $15.87   4.631%   $16.6049   $16.60   $16.60   $16.60  
  7 purchase totals = $767.80       $837.2141   $837.21   $837.15   $837.30