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 $143.92   8.583%   $156.2727   $156.27   $156.25   $156.30  
  Purchase #2 $205.94   9.668%   $225.8503   $225.85   $225.85   $225.90  
  Purchase #3 $111.68   9.679%   $122.4895   $122.49   $122.50   $122.50  
  Purchase #4 $179.49   4.725%   $187.9709   $187.97   $187.95   $188.00  
  Purchase #5 $59.65   13.157%   $67.4982   $67.50   $67.50   $67.50  
  Purchase #6 $105.36   4.698%   $110.3098   $110.31   $110.30   $110.30  
  Purchase #7 $155.63   3.576%   $161.1953   $161.20   $161.20   $161.20  
  7 purchase totals = $961.67       $1,031.5867   $1,031.59   $1,031.55   $1,031.70