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 $56.92   11.573%   $63.5074   $63.51   $63.50   $63.50  
  Purchase #2 $18.97   3.740%   $19.6795   $19.68   $19.70   $19.70  
  Purchase #3 $141.85   3.781%   $147.2133   $147.21   $147.20   $147.20  
  Purchase #4 $30.58   13.260%   $34.6349   $34.63   $34.65   $34.60  
  Purchase #5 $9.79   12.446%   $11.0085   $11.01   $11.00   $11.00  
  Purchase #6 $22.77   6.148%   $24.1699   $24.17   $24.15   $24.20  
  Purchase #7 $175.62   9.362%   $192.0615   $192.06   $192.05   $192.10  
  7 purchase totals = $456.50       $492.2750   $492.27   $492.25   $492.30