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 $183.85   9.432%   $201.1907   $201.19   $201.20   $201.20  
  Purchase #2 $203.25   8.139%   $219.7925   $219.79   $219.80   $219.80  
  Purchase #3 $89.34   12.385%   $100.4048   $100.40   $100.40   $100.40  
  Purchase #4 $175.38   12.757%   $197.7532   $197.75   $197.75   $197.80  
  Purchase #5 $237.29   3.208%   $244.9023   $244.90   $244.90   $244.90  
  Purchase #6 $91.57   4.495%   $95.6861   $95.69   $95.70   $95.70  
  Purchase #7 $186.40   13.583%   $211.7187   $211.72   $211.70   $211.70  
  7 purchase totals = $1,167.08       $1,271.4483   $1,271.44   $1,271.45   $1,271.50