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 $92.50   3.743%   $95.9623   $95.96   $95.95   $96.00  
  Purchase #2 $25.76   6.112%   $27.3345   $27.33   $27.35   $27.30  
  Purchase #3 $152.43   4.813%   $159.7665   $159.77   $159.75   $159.80  
  Purchase #4 $132.40   10.298%   $146.0346   $146.03   $146.05   $146.00  
  Purchase #5 $109.47   13.265%   $123.9912   $123.99   $124.00   $124.00  
  Purchase #6 $5.37   5.299%   $5.6546   $5.65   $5.65   $5.70  
  Purchase #7 $209.59   3.771%   $217.4936   $217.49   $217.50   $217.50  
  7 purchase totals = $727.52       $776.2373   $776.22   $776.25   $776.30