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 $73.30   7.844%   $79.0497   $79.05   $79.05   $79.00  
  Purchase #2 $68.67   13.320%   $77.8168   $77.82   $77.80   $77.80  
  Purchase #3 $7.49   4.262%   $7.8092   $7.81   $7.80   $7.80  
  Purchase #4 $25.70   10.425%   $28.3792   $28.38   $28.40   $28.40  
  Purchase #5 $34.67   4.711%   $36.3033   $36.30   $36.30   $36.30  
  Purchase #6 $127.63   7.252%   $136.8857   $136.89   $136.90   $136.90  
  Purchase #7 $101.77   9.433%   $111.37   $111.37   $111.35   $111.40  
  7 purchase totals = $439.23       $477.6139   $477.62   $477.60   $477.60