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 $201.59   8.461%   $218.6465   $218.65   $218.65   $218.60  
  Purchase #2 $54.25   11.522%   $60.5007   $60.50   $60.50   $60.50  
  Purchase #3 $195.92   12.680%   $220.7627   $220.76   $220.75   $220.80  
  Purchase #4 $54.89   8.606%   $59.6138   $59.61   $59.60   $59.60  
  Purchase #5 $148.62   11.755%   $166.0903   $166.09   $166.10   $166.10  
  Purchase #6 $173.48   11.702%   $193.7806   $193.78   $193.80   $193.80  
  Purchase #7 $225.53   8.677%   $245.0992   $245.10   $245.10   $245.10  
  7 purchase totals = $1,054.28       $1,164.4938   $1,164.49   $1,164.50   $1,164.50