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 $8.52   6.213%   $9.0493   $9.05   $9.05   $9.00  
  Purchase #2 $219.88   9.853%   $241.5448   $241.54   $241.55   $241.50  
  Purchase #3 $113.26   10.402%   $125.0413   $125.04   $125.05   $125.00  
  Purchase #4 $42.79   11.773%   $47.8277   $47.83   $47.85   $47.80  
  Purchase #5 $179.32   6.862%   $191.6249   $191.62   $191.60   $191.60  
  Purchase #6 $176.83   12.430%   $198.81   $198.81   $198.80   $198.80  
  Purchase #7 $117.27   7.730%   $126.335   $126.34   $126.35   $126.30  
  7 purchase totals = $857.87       $940.2330   $940.23   $940.25   $940.00