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 $53.75   13.526%   $61.0202   $61.02   $61.00   $61.00  
  Purchase #2 $179.98   10.336%   $198.5827   $198.58   $198.60   $198.60  
  Purchase #3 $224.53   12.221%   $251.9698   $251.97   $251.95   $252.00  
  Purchase #4 $93.74   8.545%   $101.7501   $101.75   $101.75   $101.80  
  Purchase #5 $74.73   8.363%   $80.9797   $80.98   $81.00   $81.00  
  Purchase #6 $42.76   7.277%   $45.8716   $45.87   $45.85   $45.90  
  Purchase #7 $240.52   13.571%   $273.161   $273.16   $273.15   $273.20  
  7 purchase totals = $910.01       $1,013.3351   $1,013.33   $1,013.30   $1,013.50