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 $90.31   3.564%   $93.5286   $93.53   $93.55   $93.50  
  Purchase #2 $208.36   3.107%   $214.8337   $214.83   $214.85   $214.80  
  Purchase #3 $88.76   7.797%   $95.6806   $95.68   $95.70   $95.70  
  Purchase #4 $146.92   5.511%   $155.0168   $155.02   $155.00   $155.00  
  Purchase #5 $72.44   11.658%   $80.8851   $80.89   $80.90   $80.90  
  Purchase #6 $219.25   13.176%   $248.1384   $248.14   $248.15   $248.10  
  Purchase #7 $171.65   10.461%   $189.6063   $189.61   $189.60   $189.60  
  7 purchase totals = $997.69       $1,077.6895   $1,077.70   $1,077.75   $1,077.60