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 $59.75   9.270%   $65.2888   $65.29   $65.30   $65.30  
  Purchase #2 $15.53   7.321%   $16.667   $16.67   $16.65   $16.70  
  Purchase #3 $22.74   7.259%   $24.3907   $24.39   $24.40   $24.40  
  Purchase #4 $72.54   7.153%   $77.7288   $77.73   $77.75   $77.70  
  Purchase #5 $159.64   3.398%   $165.0646   $165.06   $165.05   $165.10  
  Purchase #6 $134.73   3.774%   $139.8147   $139.81   $139.80   $139.80  
  Purchase #7 $118.87   7.424%   $127.6949   $127.69   $127.70   $127.70  
  7 purchase totals = $583.80       $616.6495   $616.64   $616.65   $616.70