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 $177.58   10.387%   $196.0252   $196.03   $196.05   $196.00  
  Purchase #2 $36.96   11.819%   $41.3283   $41.33   $41.35   $41.30  
  Purchase #3 $218.99   7.637%   $235.7143   $235.71   $235.70   $235.70  
  Purchase #4 $140.89   12.283%   $158.1955   $158.20   $158.20   $158.20  
  Purchase #5 $239.32   10.421%   $264.2595   $264.26   $264.25   $264.30  
  Purchase #6 $219.32   12.105%   $245.8687   $245.87   $245.85   $245.90  
  Purchase #7 $207.78   13.232%   $235.2734   $235.27   $235.25   $235.30  
  7 purchase totals = $1,240.84       $1,376.6649   $1,376.67   $1,376.65   $1,376.70