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 $191.86   11.643%   $214.1983   $214.20   $214.20   $214.20  
  Purchase #2 $232.52   12.398%   $261.3478   $261.35   $261.35   $261.30  
  Purchase #3 $57.48   12.869%   $64.8771   $64.88   $64.90   $64.90  
  Purchase #4 $58.44   9.255%   $63.8486   $63.85   $63.85   $63.80  
  Purchase #5 $242.53   3.601%   $251.2635   $251.26   $251.25   $251.30  
  Purchase #6 $22.31   4.787%   $23.378   $23.38   $23.40   $23.40  
  Purchase #7 $137.92   6.625%   $147.0572   $147.06   $147.05   $147.10  
  7 purchase totals = $943.06       $1,025.9705   $1,025.98   $1,026.00   $1,026.00