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 $87.80   9.315%   $95.9786   $95.98   $96.00   $96.00  
  Purchase #2 $160.86   8.662%   $174.7937   $174.79   $174.80   $174.80  
  Purchase #3 $197.60   4.372%   $206.2391   $206.24   $206.25   $206.20  
  Purchase #4 $8.87   7.555%   $9.5401   $9.54   $9.55   $9.50  
  Purchase #5 $213.90   9.810%   $234.8836   $234.88   $234.90   $234.90  
  Purchase #6 $147.34   4.638%   $154.1736   $154.17   $154.15   $154.20  
  Purchase #7 $180.34   5.381%   $190.0441   $190.04   $190.05   $190.00  
  7 purchase totals = $996.71       $1,065.6528   $1,065.64   $1,065.70   $1,065.60