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 $72.78   13.154%   $82.3535   $82.35   $82.35   $82.40  
  Purchase #2 $192.75   9.262%   $210.6025   $210.60   $210.60   $210.60  
  Purchase #3 $29.81   13.301%   $33.775   $33.78   $33.80   $33.80  
  Purchase #4 $42.95   13.356%   $48.6864   $48.69   $48.70   $48.70  
  Purchase #5 $5.86   3.417%   $6.0602   $6.06   $6.05   $6.10  
  Purchase #6 $172.98   11.575%   $193.0024   $193.00   $193.00   $193.00  
  Purchase #7 $154.54   8.258%   $167.3019   $167.30   $167.30   $167.30  
  7 purchase totals = $671.67       $741.7819   $741.78   $741.80   $741.90