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 $87.74   9.800%   $96.3385   $96.34   $96.35   $96.30  
  Purchase #2 $67.39   12.816%   $76.0267   $76.03   $76.05   $76.00  
  Purchase #3 $31.76   5.433%   $33.4855   $33.49   $33.50   $33.50  
  Purchase #4 $236.53   5.559%   $249.6787   $249.68   $249.70   $249.70  
  Purchase #5 $246.89   8.287%   $267.3498   $267.35   $267.35   $267.30  
  Purchase #6 $53.59   13.129%   $60.6258   $60.63   $60.65   $60.60  
  Purchase #7 $172.91   7.294%   $185.5221   $185.52   $185.50   $185.50  
  7 purchase totals = $896.81       $969.0271   $969.04   $969.10   $968.90