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 $89.59   5.411%   $94.4377   $94.44   $94.45   $94.40  
  Purchase #2 $94.28   3.821%   $97.8824   $97.88   $97.90   $97.90  
  Purchase #3 $154.44   8.146%   $167.0207   $167.02   $167.00   $167.00  
  Purchase #4 $235.80   9.398%   $257.9605   $257.96   $257.95   $258.00  
  Purchase #5 $182.32   7.636%   $196.242   $196.24   $196.25   $196.20  
  Purchase #6 $153.83   10.536%   $170.0375   $170.04   $170.05   $170.00  
  Purchase #7 $222.35   8.570%   $241.4054   $241.41   $241.40   $241.40  
  7 purchase totals = $1,132.61       $1,224.9862   $1,224.99   $1,225.00   $1,224.90