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 $56.86   8.314%   $61.5873   $61.59   $61.60   $61.60  
  Purchase #2 $147.32   4.126%   $153.3984   $153.40   $153.40   $153.40  
  Purchase #3 $245.37   12.730%   $276.6056   $276.61   $276.60   $276.60  
  Purchase #4 $20.35   11.480%   $22.6862   $22.69   $22.70   $22.70  
  Purchase #5 $133.49   7.185%   $143.0813   $143.08   $143.10   $143.10  
  Purchase #6 $211.41   7.693%   $227.6738   $227.67   $227.65   $227.70  
  Purchase #7 $52.72   11.119%   $58.5819   $58.58   $58.60   $58.60  
  7 purchase totals = $867.52       $943.6145   $943.62   $943.65   $943.70