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 $248.99   13.467%   $282.5215   $282.52   $282.50   $282.50  
  Purchase #2 $218.61   9.202%   $238.7265   $238.73   $238.75   $238.70  
  Purchase #3 $203.38   6.155%   $215.898   $215.90   $215.90   $215.90  
  Purchase #4 $167.25   10.591%   $184.9634   $184.96   $184.95   $185.00  
  Purchase #5 $53.55   5.456%   $56.4717   $56.47   $56.45   $56.50  
  Purchase #6 $120.89   7.528%   $129.9906   $129.99   $130.00   $130.00  
  Purchase #7 $200.48   12.845%   $226.2317   $226.23   $226.25   $226.20  
  7 purchase totals = $1,213.15       $1,334.8034   $1,334.80   $1,334.80   $1,334.80