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 $119.91   6.549%   $127.7629   $127.76   $127.75   $127.80  
  Purchase #2 $49.35   10.846%   $54.7025   $54.70   $54.70   $54.70  
  Purchase #3 $122.77   3.195%   $126.6925   $126.69   $126.70   $126.70  
  Purchase #4 $93.59   10.404%   $103.3271   $103.33   $103.35   $103.30  
  Purchase #5 $69.32   4.471%   $72.4193   $72.42   $72.40   $72.40  
  Purchase #6 $191.73   5.194%   $201.6885   $201.69   $201.70   $201.70  
  Purchase #7 $230.94   3.759%   $239.621   $239.62   $239.60   $239.60  
  7 purchase totals = $877.61       $926.2138   $926.21   $926.20   $926.20