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 $192.55   6.871%   $205.7801   $205.78   $205.80   $205.80  
  Purchase #2 $182.28   11.736%   $203.6724   $203.67   $203.65   $203.70  
  Purchase #3 $13.47   5.665%   $14.2331   $14.23   $14.25   $14.20  
  Purchase #4 $52.78   7.275%   $56.6197   $56.62   $56.60   $56.60  
  Purchase #5 $175.50   5.152%   $184.5418   $184.54   $184.55   $184.50  
  Purchase #6 $137.96   3.480%   $142.761   $142.76   $142.75   $142.80  
  Purchase #7 $48.32   8.264%   $52.3132   $52.31   $52.30   $52.30  
  7 purchase totals = $802.86       $859.9213   $859.91   $859.90   $859.90