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 $234.55   5.662%   $247.8302   $247.83   $247.85   $247.80  
  Purchase #2 $120.31   5.492%   $126.9174   $126.92   $126.90   $126.90  
  Purchase #3 $148.95   13.403%   $168.9138   $168.91   $168.90   $168.90  
  Purchase #4 $59.36   13.339%   $67.278   $67.28   $67.30   $67.30  
  Purchase #5 $161.48   9.221%   $176.3701   $176.37   $176.35   $176.40  
  Purchase #6 $135.65   13.664%   $154.1852   $154.19   $154.20   $154.20  
  Purchase #7 $108.74   5.652%   $114.886   $114.89   $114.90   $114.90  
  7 purchase totals = $969.04       $1,056.3807   $1,056.39   $1,056.40   $1,056.40