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 $22.87   9.146%   $24.9617   $24.96   $24.95   $25.00  
  Purchase #2 $176.84   7.433%   $189.9845   $189.98   $190.00   $190.00  
  Purchase #3 $96.78   6.491%   $103.062   $103.06   $103.05   $103.10  
  Purchase #4 $206.64   13.187%   $233.8896   $233.89   $233.90   $233.90  
  Purchase #5 $191.65   13.137%   $216.8271   $216.83   $216.85   $216.80  
  Purchase #6 $210.93   6.261%   $224.1363   $224.14   $224.15   $224.10  
  Purchase #7 $52.51   7.572%   $56.4861   $56.49   $56.50   $56.50  
  7 purchase totals = $958.22       $1,049.3473   $1,049.35   $1,049.40   $1,049.40