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 $210.72   12.476%   $237.0094   $237.01   $237.00   $237.00  
  Purchase #2 $162.26   5.426%   $171.0642   $171.06   $171.05   $171.10  
  Purchase #3 $28.98   3.108%   $29.8807   $29.88   $29.90   $29.90  
  Purchase #4 $186.99   4.600%   $195.5915   $195.59   $195.60   $195.60  
  Purchase #5 $240.86   7.696%   $259.3966   $259.40   $259.40   $259.40  
  Purchase #6 $179.49   12.238%   $201.456   $201.46   $201.45   $201.50  
  Purchase #7 $65.27   11.381%   $72.6984   $72.70   $72.70   $72.70  
  7 purchase totals = $1,074.57       $1,167.0968   $1,167.10   $1,167.10   $1,167.20