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 $201.96   11.867%   $225.9266   $225.93   $225.95   $225.90  
  Purchase #2 $150.75   9.450%   $164.9959   $165.00   $165.00   $165.00  
  Purchase #3 $92.35   11.824%   $103.2695   $103.27   $103.25   $103.30  
  Purchase #4 $235.51   10.574%   $260.4128   $260.41   $260.40   $260.40  
  Purchase #5 $60.87   5.129%   $63.992   $63.99   $64.00   $64.00  
  Purchase #6 $186.27   5.794%   $197.0625   $197.06   $197.05   $197.10  
  Purchase #7 $215.98   7.264%   $231.6688   $231.67   $231.65   $231.70  
  7 purchase totals = $1,143.69       $1,247.3281   $1,247.33   $1,247.30   $1,247.40