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 $54.84   9.337%   $59.9604   $59.96   $59.95   $60.00  
  Purchase #2 $90.34   3.377%   $93.3908   $93.39   $93.40   $93.40  
  Purchase #3 $9.48   4.255%   $9.8834   $9.88   $9.90   $9.90  
  Purchase #4 $81.39   3.861%   $84.5325   $84.53   $84.55   $84.50  
  Purchase #5 $23.27   3.397%   $24.0605   $24.06   $24.05   $24.10  
  Purchase #6 $159.59   5.204%   $167.8951   $167.90   $167.90   $167.90  
  Purchase #7 $61.26   4.778%   $64.187   $64.19   $64.20   $64.20  
  7 purchase totals = $480.17       $503.9097   $503.91   $503.95   $504.00