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 $161.55   7.811%   $174.1687   $174.17   $174.15   $174.20  
  Purchase #2 $26.75   11.239%   $29.7564   $29.76   $29.75   $29.80  
  Purchase #3 $52.59   10.240%   $57.9752   $57.98   $58.00   $58.00  
  Purchase #4 $55.69   7.415%   $59.8194   $59.82   $59.80   $59.80  
  Purchase #5 $48.45   5.668%   $51.1961   $51.20   $51.20   $51.20  
  Purchase #6 $143.62   11.624%   $160.3144   $160.31   $160.30   $160.30  
  Purchase #7 $245.42   8.763%   $266.9262   $266.93   $266.95   $266.90  
  7 purchase totals = $734.07       $800.1564   $800.17   $800.15   $800.20