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 $166.56   9.687%   $182.6947   $182.69   $182.70   $182.70  
  Purchase #2 $190.32   10.547%   $210.3931   $210.39   $210.40   $210.40  
  Purchase #3 $69.41   8.408%   $75.246   $75.25   $75.25   $75.20  
  Purchase #4 $222.52   3.538%   $230.3928   $230.39   $230.40   $230.40  
  Purchase #5 $92.52   9.366%   $101.1854   $101.19   $101.20   $101.20  
  Purchase #6 $237.78   7.658%   $255.9892   $255.99   $256.00   $256.00  
  Purchase #7 $9.84   3.522%   $10.1866   $10.19   $10.20   $10.20  
  7 purchase totals = $988.95       $1,066.0878   $1,066.09   $1,066.15   $1,066.10