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 $43.35   11.321%   $48.2577   $48.26   $48.25   $48.30  
  Purchase #2 $79.88   6.374%   $84.9716   $84.97   $84.95   $85.00  
  Purchase #3 $225.92   8.387%   $244.8679   $244.87   $244.85   $244.90  
  Purchase #4 $17.87   6.359%   $19.0064   $19.01   $19.00   $19.00  
  Purchase #5 $242.80   6.469%   $258.5067   $258.51   $258.50   $258.50  
  Purchase #6 $79.62   9.180%   $86.9291   $86.93   $86.95   $86.90  
  Purchase #7 $238.51   11.784%   $266.616   $266.62   $266.60   $266.60  
  7 purchase totals = $927.95       $1,009.1554   $1,009.17   $1,009.10   $1,009.20