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 $165.50   12.286%   $185.8333   $185.83   $185.85   $185.80  
  Purchase #2 $121.33   4.786%   $127.1369   $127.14   $127.15   $127.10  
  Purchase #3 $200.33   6.679%   $213.71   $213.71   $213.70   $213.70  
  Purchase #4 $8.79   5.319%   $9.2575   $9.26   $9.25   $9.30  
  Purchase #5 $107.94   7.543%   $116.0819   $116.08   $116.10   $116.10  
  Purchase #6 $218.31   3.526%   $226.0076   $226.01   $226.00   $226.00  
  Purchase #7 $172.75   5.463%   $182.1873   $182.19   $182.20   $182.20  
  7 purchase totals = $994.95       $1,060.2145   $1,060.22   $1,060.25   $1,060.20