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 $209.83   7.706%   $225.9995   $226.00   $226.00   $226.00  
  Purchase #2 $183.25   11.170%   $203.719   $203.72   $203.70   $203.70  
  Purchase #3 $213.79   5.846%   $226.2882   $226.29   $226.30   $226.30  
  Purchase #4 $125.31   11.159%   $139.2933   $139.29   $139.30   $139.30  
  Purchase #5 $118.61   8.542%   $128.7417   $128.74   $128.75   $128.70  
  Purchase #6 $208.33   8.815%   $226.6943   $226.69   $226.70   $226.70  
  Purchase #7 $159.97   10.162%   $176.2262   $176.23   $176.25   $176.20  
  7 purchase totals = $1,219.09       $1,326.9622   $1,326.96   $1,327.00   $1,326.90