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 $98.85   11.104%   $109.8263   $109.83   $109.85   $109.80  
  Purchase #2 $184.94   11.854%   $206.8628   $206.86   $206.85   $206.90  
  Purchase #3 $51.28   11.236%   $57.0418   $57.04   $57.05   $57.00  
  Purchase #4 $125.72   4.181%   $130.9764   $130.98   $131.00   $131.00  
  Purchase #5 $84.93   7.349%   $91.1715   $91.17   $91.15   $91.20  
  Purchase #6 $243.44   3.445%   $251.8265   $251.83   $251.85   $251.80  
  Purchase #7 $87.79   8.506%   $95.2574   $95.26   $95.25   $95.30  
  7 purchase totals = $876.95       $942.9627   $942.97   $943.00   $943.00