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 $207.62   3.486%   $214.8576   $214.86   $214.85   $214.90  
  Purchase #2 $135.56   10.557%   $149.8711   $149.87   $149.85   $149.90  
  Purchase #3 $13.68   6.482%   $14.5667   $14.57   $14.55   $14.60  
  Purchase #4 $102.49   3.470%   $106.0464   $106.05   $106.05   $106.00  
  Purchase #5 $61.65   7.640%   $66.3601   $66.36   $66.35   $66.40  
  Purchase #6 $237.28   3.455%   $245.478   $245.48   $245.50   $245.50  
  Purchase #7 $192.85   8.418%   $209.0841   $209.08   $209.10   $209.10  
  7 purchase totals = $951.13       $1,006.2640   $1,006.27   $1,006.25   $1,006.40