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 $57.64   10.274%   $63.5619   $63.56   $63.55   $63.60  
  Purchase #2 $209.57   9.820%   $230.1498   $230.15   $230.15   $230.10  
  Purchase #3 $21.94   9.277%   $23.9754   $23.98   $24.00   $24.00  
  Purchase #4 $145.31   5.808%   $153.7496   $153.75   $153.75   $153.70  
  Purchase #5 $240.95   11.570%   $268.8279   $268.83   $268.85   $268.80  
  Purchase #6 $82.55   3.804%   $85.6902   $85.69   $85.70   $85.70  
  Purchase #7 $104.70   4.808%   $109.734   $109.73   $109.75   $109.70  
  7 purchase totals = $862.66       $935.6888   $935.69   $935.75   $935.60