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 $217.73   13.225%   $246.5248   $246.52   $246.50   $246.50  
  Purchase #2 $201.53   3.236%   $208.0515   $208.05   $208.05   $208.10  
  Purchase #3 $51.64   9.708%   $56.6532   $56.65   $56.65   $56.70  
  Purchase #4 $32.62   4.140%   $33.9705   $33.97   $33.95   $34.00  
  Purchase #5 $165.52   5.301%   $174.2942   $174.29   $174.30   $174.30  
  Purchase #6 $146.53   11.253%   $163.019   $163.02   $163.00   $163.00  
  Purchase #7 $166.49   9.438%   $182.2033   $182.20   $182.20   $182.20  
  7 purchase totals = $982.06       $1,064.7165   $1,064.70   $1,064.65   $1,064.80