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 $56.31   8.241%   $60.9505   $60.95   $60.95   $61.00  
  Purchase #2 $235.91   4.730%   $247.0685   $247.07   $247.05   $247.10  
  Purchase #3 $210.81   10.513%   $232.9725   $232.97   $232.95   $233.00  
  Purchase #4 $124.28   5.676%   $131.3341   $131.33   $131.35   $131.30  
  Purchase #5 $10.73   12.573%   $12.0791   $12.08   $12.10   $12.10  
  Purchase #6 $130.61   10.275%   $144.0302   $144.03   $144.05   $144.00  
  Purchase #7 $228.83   8.669%   $248.6673   $248.67   $248.65   $248.70  
  7 purchase totals = $997.48       $1,077.1022   $1,077.10   $1,077.10   $1,077.20