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 $225.50   3.573%   $233.5571   $233.56   $233.55   $233.60  
  Purchase #2 $114.80   6.531%   $122.2976   $122.30   $122.30   $122.30  
  Purchase #3 $165.52   13.509%   $187.8801   $187.88   $187.90   $187.90  
  Purchase #4 $44.83   5.145%   $47.1365   $47.14   $47.15   $47.10  
  Purchase #5 $53.51   12.661%   $60.2849   $60.28   $60.30   $60.30  
  Purchase #6 $188.56   9.501%   $206.4751   $206.48   $206.50   $206.50  
  Purchase #7 $250.36   6.666%   $267.049   $267.05   $267.05   $267.00  
  7 purchase totals = $1,043.08       $1,124.6803   $1,124.69   $1,124.75   $1,124.70