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 $22.96   6.809%   $24.5233   $24.52   $24.50   $24.50  
  Purchase #2 $226.76   11.518%   $252.8782   $252.88   $252.90   $252.90  
  Purchase #3 $68.27   12.589%   $76.8645   $76.86   $76.85   $76.90  
  Purchase #4 $146.59   10.555%   $162.0626   $162.06   $162.05   $162.10  
  Purchase #5 $175.48   13.328%   $198.868   $198.87   $198.85   $198.90  
  Purchase #6 $134.91   12.599%   $151.9073   $151.91   $151.90   $151.90  
  Purchase #7 $120.80   6.571%   $128.7378   $128.74   $128.75   $128.70  
  7 purchase totals = $895.77       $995.8417   $995.84   $995.80   $995.90