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 $219.61   8.497%   $238.2703   $238.27   $238.25   $238.30  
  Purchase #2 $147.97   13.328%   $167.6914   $167.69   $167.70   $167.70  
  Purchase #3 $8.71   11.509%   $9.7124   $9.71   $9.70   $9.70  
  Purchase #4 $245.76   9.139%   $268.22   $268.22   $268.20   $268.20  
  Purchase #5 $171.94   7.286%   $184.4675   $184.47   $184.45   $184.50  
  Purchase #6 $181.81   13.372%   $206.1216   $206.12   $206.10   $206.10  
  Purchase #7 $86.89   10.227%   $95.7762   $95.78   $95.80   $95.80  
  7 purchase totals = $1,062.69       $1,170.2594   $1,170.26   $1,170.20   $1,170.30