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 $54.25   12.517%   $61.0405   $61.04   $61.05   $61.00  
  Purchase #2 $197.88   13.757%   $225.1024   $225.10   $225.10   $225.10  
  Purchase #3 $15.69   4.233%   $16.3542   $16.35   $16.35   $16.40  
  Purchase #4 $86.96   5.520%   $91.7602   $91.76   $91.75   $91.80  
  Purchase #5 $160.96   11.342%   $179.2161   $179.22   $179.20   $179.20  
  Purchase #6 $64.35   11.493%   $71.7457   $71.75   $71.75   $71.70  
  Purchase #7 $228.29   11.117%   $253.669   $253.67   $253.65   $253.70  
  7 purchase totals = $808.38       $898.8881   $898.89   $898.85   $898.90