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 $54.39   8.705%   $59.1246   $59.12   $59.10   $59.10  
  Purchase #2 $230.82   13.528%   $262.0453   $262.05   $262.05   $262.00  
  Purchase #3 $179.44   7.686%   $193.2318   $193.23   $193.25   $193.20  
  Purchase #4 $50.85   13.572%   $57.7514   $57.75   $57.75   $57.80  
  Purchase #5 $51.34   6.583%   $54.7197   $54.72   $54.70   $54.70  
  Purchase #6 $157.99   7.732%   $170.2058   $170.21   $170.20   $170.20  
  Purchase #7 $188.42   12.173%   $211.3564   $211.36   $211.35   $211.40  
  7 purchase totals = $913.25       $1,008.4350   $1,008.44   $1,008.40   $1,008.40