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 $71.69   5.794%   $75.8437   $75.84   $75.85   $75.80  
  Purchase #2 $127.98   12.803%   $144.3653   $144.37   $144.35   $144.40  
  Purchase #3 $117.97   13.212%   $133.5562   $133.56   $133.55   $133.60  
  Purchase #4 $162.29   11.666%   $181.2228   $181.22   $181.20   $181.20  
  Purchase #5 $147.98   11.710%   $165.3085   $165.31   $165.30   $165.30  
  Purchase #6 $248.78   12.871%   $280.8005   $280.80   $280.80   $280.80  
  Purchase #7 $172.27   5.686%   $182.0653   $182.07   $182.05   $182.10  
  7 purchase totals = $1,048.96       $1,163.1623   $1,163.17   $1,163.10   $1,163.20