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 $56.57   9.527%   $61.9594   $61.96   $61.95   $62.00  
  Purchase #2 $140.37   4.269%   $146.3624   $146.36   $146.35   $146.40  
  Purchase #3 $109.59   9.643%   $120.1578   $120.16   $120.15   $120.20  
  Purchase #4 $35.32   5.136%   $37.134   $37.13   $37.15   $37.10  
  Purchase #5 $62.40   13.129%   $70.5925   $70.59   $70.60   $70.60  
  Purchase #6 $151.77   5.294%   $159.8047   $159.80   $159.80   $159.80  
  Purchase #7 $200.45   9.740%   $219.9738   $219.97   $219.95   $220.00  
  7 purchase totals = $756.47       $815.9846   $815.97   $815.95   $816.10