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 $61.84   9.316%   $67.601   $67.60   $67.60   $67.60  
  Purchase #2 $10.80   5.656%   $11.4108   $11.41   $11.40   $11.40  
  Purchase #3 $157.50   11.641%   $175.8346   $175.83   $175.85   $175.80  
  Purchase #4 $65.46   7.464%   $70.3459   $70.35   $70.35   $70.30  
  Purchase #5 $235.98   9.202%   $257.6949   $257.69   $257.70   $257.70  
  Purchase #6 $177.70   11.532%   $198.1924   $198.19   $198.20   $198.20  
  Purchase #7 $192.67   12.114%   $216.01   $216.01   $216.00   $216.00  
  7 purchase totals = $901.95       $997.0896   $997.08   $997.10   $997.00