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 $129.51   10.572%   $143.2018   $143.20   $143.20   $143.20  
  Purchase #2 $173.47   11.581%   $193.5596   $193.56   $193.55   $193.60  
  Purchase #3 $12.30   9.392%   $13.4552   $13.46   $13.45   $13.50  
  Purchase #4 $179.36   4.169%   $186.8375   $186.84   $186.85   $186.80  
  Purchase #5 $25.54   3.402%   $26.4089   $26.41   $26.40   $26.40  
  Purchase #6 $206.89   13.241%   $234.2843   $234.28   $234.30   $234.30  
  Purchase #7 $224.54   12.773%   $253.2205   $253.22   $253.20   $253.20  
  7 purchase totals = $951.61       $1,050.9678   $1,050.97   $1,050.95   $1,051.00