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 $224.93   3.847%   $233.5831   $233.58   $233.60   $233.60  
  Purchase #2 $101.57   13.588%   $115.3713   $115.37   $115.35   $115.40  
  Purchase #3 $70.96   7.252%   $76.106   $76.11   $76.10   $76.10  
  Purchase #4 $173.36   5.506%   $182.9052   $182.91   $182.90   $182.90  
  Purchase #5 $206.70   7.334%   $221.8594   $221.86   $221.85   $221.90  
  Purchase #6 $19.68   13.468%   $22.3305   $22.33   $22.35   $22.30  
  Purchase #7 $226.59   6.205%   $240.6499   $240.65   $240.65   $240.60  
  7 purchase totals = $1,023.79       $1,092.8054   $1,092.81   $1,092.80   $1,092.80