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 $88.81   6.636%   $94.7034   $94.70   $94.70   $94.70  
  Purchase #2 $76.69   4.273%   $79.967   $79.97   $79.95   $80.00  
  Purchase #3 $245.34   7.210%   $263.029   $263.03   $263.05   $263.00  
  Purchase #4 $36.53   6.630%   $38.9519   $38.95   $38.95   $39.00  
  Purchase #5 $182.75   3.223%   $188.64   $188.64   $188.65   $188.60  
  Purchase #6 $61.31   4.629%   $64.148   $64.15   $64.15   $64.10  
  Purchase #7 $12.95   10.789%   $14.3472   $14.35   $14.35   $14.30  
  7 purchase totals = $704.38       $743.7865   $743.79   $743.80   $743.70