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 $151.76   5.819%   $160.5909   $160.59   $160.60   $160.60  
  Purchase #2 $180.95   5.193%   $190.3467   $190.35   $190.35   $190.30  
  Purchase #3 $48.81   8.540%   $52.9784   $52.98   $53.00   $53.00  
  Purchase #4 $214.35   12.245%   $240.5972   $240.60   $240.60   $240.60  
  Purchase #5 $227.43   11.425%   $253.4139   $253.41   $253.40   $253.40  
  Purchase #6 $246.47   7.654%   $265.3348   $265.33   $265.35   $265.30  
  Purchase #7 $37.25   8.278%   $40.3336   $40.33   $40.35   $40.30  
  7 purchase totals = $1,107.02       $1,203.5955   $1,203.59   $1,203.65   $1,203.50